


Code Name: SENTINEL

by uwa-so-frisk (disillusionist9)



Series: Undertale: SINonymous [2]
Category: Undertale (Video Game)
Genre: Alcohol, Alternate Universe - Mobtale, Alternate Universe - Underfell, Alternative Universe - Mobfell, Claiming Bites, Consensual, Denial of Feelings, Drinking, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), F/F, F/M, Gender-Neutral Pronouns, Implied/Referenced Mind Control, Light Bondage, M/M, Minor Character Death, Mob Boss Papyrus, Mobfell, Murder, Name-Calling, Possessive Behavior, Reader Is Not Chara, Reader Is Not Frisk, Reader-Insert, Reader-Interactive, Rough Sex, Smoking, Soul Bond, Souls, The Void, Touch-Starved
Language: English
Status: In-Progress
Published: 2018-01-14
Updated: 2018-04-01
Packaged: 2019-03-04 21:55:41
Rating: Explicit
Warnings: Graphic Depictions Of Violence
Chapters: 38
Words: 31,731
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13373838
Author URL: https://archiveofourown.org/users/disillusionist9/pseuds/uwa-so-frisk
Summary: You are Sentinel, a human involved with the monster mob for the last year of your life. It's taken that time to gain the trust of Boss, Undyne, Grillby, and the rest of the monsters, the only human included in their inner circle. But this only makes you a bigger target to the rival clans and mobs. Someone is working to force the monsters back to the Underground, the prison of their once and former King, and will stop at nothing to do it.You'd give your very Soul to keep it from happening.- Reader is nicknamed and gender neutral pronouns used where necessary -





	1. The Sentinel at Death's Doorstep

“get’n here, sweetheart.”

Stumbling over the ledge, you hold the shreds of your shirt to your chest, the skeleton beside you pressing his jacket into the wound on your side. The buckle on one of your shoes is ripped and hitting the top of your foot in time with your staggered steps. If not for Sans, you’d fall over entirely.

“grillby! boss!”

You wince at how loud his voice is, right next to your ear. Your eyes are closed against the bright lights of whatever safe house he’d brought you to. There’s some commotion around you and your feet sweep out from under you.

“Explain.” It’s Boss’s voice, but you’ve never heard it that quiet.

Grillby’s voice sparks somewhere to your right. “Clear that table there! No, fucking  _ move _ you worthless shit, make  _ room _ !” Stars, he sounds rough. 

Sans starts talking fast, so fast that his Brooklyn accent slurs his words into a muddled mess you can’t rightly follow, punctuated with swears and curses so vile you want to laugh. You love it when he swears like that. The way his gold fang flashes in the light from his ever-present cigar or cigarette, the slight tinge of red on his zygomatic bones as he works himself nearly to a frothing frenzy. You want to laugh, to hold him close, but you can’t. Now’s not the time, since you’re fairly sure one of your ribs is inside of your lung. It’s not that you need to listen, anyway. You lived this story.

When your body is settled onto a hard surface and stretched out, you cry out and try to curl into yourself. Hands all around you stop you and you whimper. Sans’s jacket is still pressed into your side and you wonder how he managed it as Boss carried you. 

“Did you shortcut here, brother?”

“yes, boss.”

“Did anyone see you leave?”

“...i don’t know, boss.”

Boss sighs. “Nothing to be done for that, I suppose. Grillby. Status.”

The fire elemental’s hands keep running over you, not touching your skin but hovering above it. You’ve seen him do this to countless monsters during your time with Boss and the rest of his mob, and you distinctly remember not wanting it done to you  _ ever _ . It stings like a motherfucker. You’re sure it would feel worse to have his cauterizing healing magic on you when you didn’t already feel like your Soul was trying to escape your dying body.

Eyes still screwed shut, you can still make out the changing purple flame of the monster next to you. Focus on breathing. Take in just enough air to not -  _ oh fuck that hurts - _ so much for not aggravating your broken ribs.

Your hand flutters over the edge of the table in a spasm of pain, and a skull presses into your palm in an instant.

Cracking one eye open, you try to smile at Sans. His mouth is turned down into a deep frown, creases pressed into the sides of his eye sockets where humans get crow’s feet. Even his fang looks less lustrous, but that could also be because of the dried blood flecking the surface of most of his teeth. Every sharpened edge proves how very dead your assaulters are.

“They didn’t-” you start to say, cut off by a spasm of pain. They’d grabbed you by the throat and taken you to that alley, and you can certainly feel the bruising as you try to speak.

“shh, sweetheart, don’t talk yet.”

“Did they hurt you?” you cough out before your voice fails you again.

Sans’s red irises widen and contract in a blink. He shakes his head just enough for you to understand. No. He hurt them before they had a chance to touch him. Good. You worried about him.

The shine of his red sweat in the fluorescent light above you catches your eye, and you want to reach over to wipe it away. His face turns into your palm so your fingers brush over his closed lids, his teeth pressed into the pulse in your wrist. You watch him, distracted by what’s happening around you.

A spark of Grillby’s magic flares at the edge of your vision and you can hear the crack inside you before you feel it.

“God DAMNIT!” you screech, and fresh tears swim in your eyes. Coughs wrack your body, and while you’re barely aware that you can cough again without feeling like you’re getting stabbed freshly each time, it still fucking  _ hurts _ . “God fucking  _ damnit. _ ”

Strong arms hold your feet down so you can’t thrash. A pair of hands ending in claws that dig through your shirt and graze your shoulders keep your torso down, too. Your eyes are closed again and the last thing you feel before passing out is Sans’s hand against your sternum.

**Notes for the Chapter:**

> [yell at me on tumblr](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  
> 
> Welcome to Mobfell. I did not create this AU.


	2. The Growled Vow

**Summary for the Chapter:**

> The beginning of your recuperation.

The light filtering through your eyelids is much softer when you wake next. And, while you can feel ribs poking into you, they aren’t your own this time.

Sans wakes up the moment you stir, if he was asleep at all. The lines of his body are tense and you know without looking behind you that he’s still frowning as much as he was the last time you were awake. Your eyes feel puffy and don’t adjust to the darkness right away. It’s not a room you recognize, but the knick knacks on the bedside table and the jacket draped over a single chair are familiar. Whatever safe house this is, this is Sans’s room. Sparsely decorated, impersonal, but to you it feels like home knowing whose it is. 

Light creeping under the crack between the door and the floor is just bright enough to shine off the stones in his cufflinks on the table. The cufflinks you remember giving to him on his birthday a few months ago. Stars, that feels like an age and a half ago. 

“sweetheart.”

He sounds uncertain. Quiet. 

Afraid.

“Sans,” you sigh, pressing back into him. As pokey as he can be, his weight and warmth at your back is welcome. Your throat hurts like a mother still, so you try to tell him with your body what your words can’t manage just yet.

There’s a breath that ruffles against your neck and his body relaxes into you again. The hand that was tentatively resting against your ribs, the same place his hand was pressing his jacket to before, moves up to rest against your sternum.

Never had you woken up in his bed like this before. It’s...nice. You wish it hadn’t taken you nearly dying for it to happen, but that’s par for the course for the two of you.

“Sans?”

His thumb halts it’s slow back and forth over your sternum. “what d’you need, sweetheart?”

Gingerly you turn to face him, his hand pulling back as you do. “I don’t know. I...can you tell me what’s happened since you brought me here?”

The tightness in his face you recall from the night before is still there, dancing at the edge of his fanged smile. Without the blood from your assaulters he looks more himself, the Sans you’ve been working alongside for months now, but no less dangerous. You shiver at the sight of him in the low light and his hand stutters on the mattress in front of you, inching closer to your hand though he doesn’t take it. You wish he would. 

“all business with you, eh?” he says.

You shrug at that. You aren’t one of the best informants for Boss’s mob without extensive credentials. And you’re fairly certain those credentials have been compromised.

Sans sighs and sits up a bit in the bed, turning over to turn on a small dingy lamp, the chain rattling against his bones. When you start sitting up next to him, he doesn’t stop you, but he does watch you closely. As sore as you are, and as close as you were to dying by the docks, you both know Grillby’s magic is better than any trip to the hospital. What you need is time, more than anything.

The button up shirt covering you now isn’t the one that was ripped when the first knifepoint slipped past your defense efforts. You don’t have to ask whose it is; it smells exactly like Sans, and it’s large enough that you have to roll the sleeves three times to free your hands, and you know if you stood it would reach almost to your knees.

His fingers scrape against the back of his skull. “honestly, boss is the one to talk to ‘bout that. for what you wanna know.”

“I figured,” you sigh, wrapping your arms around yourself. “I caused a lot of shit last night.”

The self-sorry words are barely out of your mouth before he’s on you. Well, not literally, he’s carefully getting as close to you as he can without touching you. Now that you’re awake and lucid he seems reluctant to touch you again.

The gold of his fang shines in the low lamplight and the red irises above it bore into you.

“nothin’ ‘bout last night was your fault, sweetheart,” he snarls. “it’s the fuckin’ rat’s fault. i’ll fuckin’ rip out their throat with my bare hands when we fin’ out who gave you away.”

A memory of blood over his mouth mixed with the murderous intent in his eyes shoots heat through you.

You don’t flinch or back away from him. There’s no danger to you in this moment. Rather, you feel safer than you have for weeks. You’re used to this, this hot and cold from the skeleton monster, and can see through his bluster. This isn't bluster. 

This is a promise, a vow, something dark and menacing.

Your mouth is a hard line, your shoulders stone as you match him gaze for gaze and say, “Save some of them for me when you’re done.”

Sans smiles for the first time since he found you half-dead. It stretches far enough you can see dozens of sharp teeth filed to points, and the static in the air lifts the hair on your neck and arms.

“no promises, sweetheart.”

**Notes for the Chapter:**

> [link to my hovel i mean tumblr](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  
> 
>  _Holy shit_ I did not expect this type of response so soon, I am blown away.


	3. The Dapper Don

**Summary for the Chapter:**

> Boss makes time for you.

“NO LEADS YET? THIS IS A DISGRACE, WHAT DO I PAY YOU IMBECILES FOR IF NOT TO GATHER INFORMATION.”

“What part of the city do you need me in, next, Boss?”

You walk towards the Boss’s office as he meets with one of his most enthusiastic leaders, Undyne, their voices carrying easily down the hallway. The walkway outside of the room is narrow, with metal fencing protecting those on it from falling a good two stories. The safe house is a repurposed warehouse you suspect is part of the vehicle assembly front that brings in a good portion of the mob’s unlaundered income. Who knew monster magic was the key to unlocking so much in mechanics? 

“UNDYNE, I NEED YOU HERE FIRST. THE NEXT GROUP ISN’T LEAVING UNTIL - AH, HUMAN. I SEE YOU’VE AWAKENED.”

The labored breathing of the underlings on the floor isn’t audible until you enter the room. Undyne nods to you in respect once as you step in, which you return. Your interactions with her have not always been pleasant. It still amuses you all it took was a sweaty sparring match and a drunken poker game with her to gain her trust. Even if you can’t see with her eye to eye, literally and figuratively because the woman is a  _ giant _ almost as tall as Boss, there’s a tempered affection between you.

The Boss, Papyrus, leans against the front of his desk with his sleeves rolled up to his elbows and tie loosened. You know he hates wailing into people because of the way it creases his clothes. The few on the ground must have really fucked up for him to willingly roll his sleeves. 

He wipes at his hands with a small white towel with pink stains, throwing it to the floor next to the humans and monsters you don’t recognize, and turns his attention to you.

“ARE YOU MENDING, HUMAN?”

Your face is still stoney, but when you incline your head in the affirmative you make sure to put grateful inflection in your voice. “Yes, sir. Grillby is a wonder.”

“HE IS. UNDYNE, PLEASE REMOVE THESE CRETINS FROM MY SIGHT. DO NOT RETURN UNTIL I SEND FOR YOU AGAIN, AND DO NOT LEAVE THE SAFE HOUSE. ARE WE CLEAR?”

“Yes, boss,” Undyne grumbles, cracking her knuckles as she takes a step towards the underlings. Ugh. You wrinkle your nose. One of them definitely pissed themselves.

Boss holds out an arm to stop her before she can cross his path to the bloodied but breathing bodies. “ARE. WE. CLEAR, UNDYNE?”

A light flush colors the fish woman’s cheeks, tingeing the blue a shade closer to purple. She bares her fangs and narrows her single eye, but backs down. Her voice is clipped but submissive. “Yes, boss.”

“GOOD.” Papyrus lowers his arm. “I NEED MY BEST FOR THIS, UNDYNE, SO I NEED YOU. YOU WILL NOT FAIL ME.”

The compliment that borders on a threat changes the woman’s demeanor immediately. Undyne throws the bodies over her shoulders and moves to leave the room. You realize you don’t care who those people are, or were based off their rather lifeless states.

“MY BROTHER IS NOT WITH YOU?”

Boss’s voice drags your attention away from the door. “No, sir. He’s resting while he waits for your orders.”

“HMM. VERY WELL. I’LL DEAL WITH HIM LATER.” Rolling down his sleeves, you can see a different kind of distaste color his features than the absolute hatred directed towards the underlings. “UGH. I LIKED THIS SHIRT, TOO.”

Your mouth twitches slightly at the monster’s aggravation. The gravity of the situation doesn’t allow you to relax fully, though, standing near the door with your arms behind your back, standing at ease before him. It’s not often Boss allows his brother to rest and boost his HP without a passing snide comment. That alone proves the shit has absolutely hit the fan.

“I NEED YOU TO TELL ME EVERYTHING YOU REMEMBER, SENTINEL.”

The code name you’d carried for almost a year snaps you to full attention. It’s a word laced with power, with magic, a contract between you and the man slowly fixing his blood red tie. The color reminds you of the lights in Sans’s eyes, but you will yourself to fight distraction.

“Yes, boss,” you say. “Where should I begin?”

Boss steps away from his desk, his full height dwarfing you, and moves around to sit behind the impressively large handcrafted wonder that is his battlestation. You wait patiently for his next orders. He opens a drawer and stares into it for several breaths before sighing and taking out what was inside. A crystal decanter with amber liquid emerges followed by two tumblers and a slim black journal.

“I HOPED WHEN WE ERADICATED THE INFLUENCE OF THE MORESBY CLAN LAST MONTH THAT THIS FOUL BUSINESS WOULD BE BEHIND US. MY HOPE WAS MISPLACED.” Without asking, he pours you a glass that’s as full as his own. A wave of his hand invites you to sit across from him, and you oblige. “START AS FAR BACK AS YOU NEED TO, SENTINEL. I HAVE THE TIME.”

“I don’t think we do, boss,” you say, forcing down the sarcasm bubbling up inside. It’s harder to suppress when you still feel like you were hit by a freight train. You stare at the whiskey for all of a second before you gulp it down, wiping your mouth with the back of your hand. “You’ll need to gather it the hard way.”

The bone beneath Boss’s eye twitches. “I’D RATHER NOT RESORT TO SUCH ACTION, SENTINEL.”

You’re taken aback. Boss had removed and touched your Soul more times than you care to admit, mostly in an effort to pass along information thoroughly and discreetly, though the first time was more or less to verify your loyalty. But no one questions Boss, especially when his dander is up like it is now.

You poke the tip of your tongue out to catch a drop of whiskey you can feel on your lips. “As you say, Boss.”

**Notes for the Chapter:**

> [this is a link to tumblr where my garbage fire lights the way](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  
> 
> Seriously, you guys rock my world.


	4. The Shocking Report

**Summary for the Chapter:**

> You show a little skin.

“The thugs what jumped me are - were - members of the Moresby’s as far as I can wager,” you say, clutching your second drink between your hands. The alcohol is taking the edge off the pain. “I’d been trailing their friend, that Fjoler sonuvabitch, since we found out he’s the one who hit our connection at the Plaza. Burgerpants didn’t deserve to go like that. Basic shit. Too bad for them and good for us they were stupid bastards who are shit at shaking a person tailing them.”

Boss’s mouth twitches in amusement behind his steepled fingers, but he doesn’t make a comment. You both know the only people who would have any luck shaking you are mages and monsters, which are in short supply in enemy clans. Boss has used you to make sure of that.

“There’s some sort of operation they’re hoping to capture a monster for.”

The scrape of Boss’s sharpened fingertips against the glass atop his desk makes you cringe. He doesn’t apologize, but he doesn’t do it again.

“WHAT SORT OF OPERATION?”

“Souls, of course. What else? Same song and dance as before you all were stuffed under a goddamned mountain.”

“I SEE. AND, YOU’RE CORRECT, THE THUGS WERE MORESBY’S.” For the first time you notice the pocket watch Boss has on his desk. You didn’t notice it sitting atop a bloody pile of clothes. Boss notices what you’re staring at. “MY LAZY BONES OF A BROTHER MANAGED TO BRING THAT BEFORE THE BODIES WERE REMOVED FROM THE SCENE. DOGGO WILL TRACK WHAT HE CAN. CONTINUE.”

The curt explanation is more than you’d hoped for, and the barked order to continue snaps you out of your staring. You stare into space as you talk and can hear the scraping of his pen in the leatherbound journal as he takes notes.

“They obviously are close to what they think will seal you back in the Underground,” you say. You’re rushing now, but you know he can keep up. “I don’t know who they have, I don’t know all who’s missing or unaccounted for of ours, but I could smell the Dust on them before they threw the first punch.”

“HOW DID THEY MANAGE TO LAND EVEN A SINGLE HIT, SENTINEL?”

You force away the desire to withdraw into yourself.

Under the command of your code name you are very aware of the mixture of negative emotion radiating from Boss. When you told Sans you were going to see him as soon as you could change your clothes, his feral grin fell back into the grimace you were starting to hate. The grin suits him far better, whether it was from one of his shitty jokes or from bloodlust. You don’t know which one of those you like more.

“jus’ be careful, alright?” he had said to you, hands stuffed into the pockets of his tailored suit pants. “you call me if you need me.”

A year ago, you would have scoffed at Sans’s tone and posture, flipped him the bird, and assured him you can take care of yourself. Now? Now you stand a few feet apart from the man, the monster, who’d saved your bloody hide from death and who still wore the cufflinks you bought him every day. This is the moment he’d been worried about, the moment Boss’s concern for your well-being fell away, and his possessive and controlling nature returned.

It’s hard to predict a monster with his LV.

“Taser, Boss.” You unbutton your shirt from the top so you can push it down over your shoulder, showing him the scorch marks from a few taser blasts done at too close a range. The highest one is burned into the soft skin below your earlobe, a bruise blooming all around it.

The suit you’d put together from the wardrobe in Burgerpants - Felix’s - old room is bulky on your frame. His height is - fuck, _was_ \- impressive just like Boss and Undyne and so many other monsters in the clan. It almost feels wrong to wear his things, but his mate, Guy, had all but thrust them at you when he realized you didn’t have anything to wear in this safehouse apart from the rags you wore in.

Boss leans closer, pushing your shirt aside a bit more. The strap of the black tank top beneath covers half of a bite mark, but his fingertips are tracing the marks on your neck. You haven’t seen a mirror yet, but you have a feeling you know what he sees.

“THEIR FUCKING SIGIL,” Boss says with venom, dark orange magic spittle flying from his mouth. “MAKING MAGIC INFUSED TASERS, NOW, ARE THEY?”

Boss tears his hand away, pressing it to his forehead with a long-suffering sigh. “LEAVE ME FOR NOW, SENTINEL. TRACK DOWN UNDYNE! SHE’S LIKELY CAVORTING WITH THAT SCIENTIST. AND TELL HER TO BRING THE CANINE UNIT WITH HER!”

**Notes for the Chapter:**

> [this is a link to tumblr where my garbage fire lights the way](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> _**mobster voice** youse...youse guys is all valid...all'a youse._
> 
> I could be persuaded to post more if the angst starts rattling your bones...


	5. The Good Doctors

Undyne is with Alphys and Gaster as Boss suspected, pacing around the room like she’s trying to wear a hole in her shoes or the floor, whichever happens first. The dark red of her hair swings back and forth across her back as she paces, head down. The scientists are poring over blueprints and hundreds of documents. 

Alphys wrings her hands and watches Undyne each time she passes in front of her field of vision, the eyes behind her glasses damp and nervous. How two such polar opposites worked as a pair as well as they did, you didn’t understand. The two of them are blind as eyeless rats when it came to each other.

Though, you’re hardly a good authority on that. Nearly ten months of skirting your feelings for the Boss’s brother and the most you’d done to show the depth of affection was give him fucking cufflinks. Even in the privacy of your own head you can’t admit it.

_ Ah, but it’s not private there either, is it? _

To shut up the nagging voice, you snap, “Undyne. Boss sent me to tell you he has something for you to do.”

“FINALLY!” the fish woman exclaims, throwing her hands into the air and turning around so fast she gives you whiplash just watching her.

“Grab the canine unit when you go up,” you call after her sprinting form. The emergency lights in the concrete corridor cast her scales in an eerie light, as if she is swimming underwater instead of running on dry land. She throws a hand up as she runs to let you know she heard you.

“Greetings, Sentinel.”

“Hey, there, Dr. Gaster,” you say, greeting the soft spoken monster. He pats a stool next to him with one of his hands, the hole in his palm catching your eye the same as it does every time. “Sorry, but I need to find Grillby, actually. Any clue where he is?”

The doctor gets a faraway look in his cracked eye sockets, the colored irises within flickering like an old-school film reel for a few seconds. Alphys smiles at you tentatively, and you nod in acknowledgement. You aren’t that close to her, the shy monster only around you for brief moments and in larger groups, but she’s far more delicate than most of the monsters in the mob. Her EXP and LV is ground level whereas her peers boast penthouse numbers. It makes her saner, calmer, but far less sociable.

“Grillby is off-premises,” Gaster says, the clicking in his voice subdued today. Must not have had to mess with the Void much lately.

You sigh in frustration. There aren’t many monsters who know enough about human anatomy to check on your progress. And you  _ really _ don’t want to approach Toriel. Your temper is short enough without dealing with the glares of the goat woman, and you  _ will not _ owe her any fucking favors. Ever. One offhand mention of her relationship with the Bergentrückung your first month here and you’ve lived on her shitlist since.

“I’m - uh, I’m glad you’re back, Sentinel,” Alphys says. If Gaster is quiet you can barely hear Alphys.

“Good to be back, Doc. Been a while since I was home.”

“W-well this isn’t quite home b-but…” Alphys trails off, dipping her head. 

Your mouth, its little patient smile doused with that one sentence, thins into a line. “Yeah. Thanks anyway, Gaster. See you guys around.”

Shoving your hands into the pockets of the borrowed pants, you hunch your shoulders and stroll down the corridor Undyne sprinted through. You really want to take a shower; there’s still dried blood on your body where it wasn’t wiped away while they were fixing you up. You also haven’t taken the time to sit down and asses your own wounds, if you had new scars, any of that. The way your skin itches and your Soul weighs heavy in your chest, you don’t feel like you have the time to do any of that.

You know it’s shitty to walk away from the doctors like that without catching up, but it was shitty of Alphys to bring up the fucking reason why you’re not all together in the posh mansion up river. It’s not like the local police don’t know that’s the monster clan’s main forum, and the opulate property is nothing close to under the radar, but several monsters still blamed you for the breach of security that compromised it.

It’s been two months since the last stand with Moresby’s on the lawns outside the mansion, but it still reeked of monster Dust and human blood, and the mess got big enough that the human federal government is involved. Well, it was what everyone thought was the last stand. These safe houses were only meant to be until things calmed down out there. Apparently that was further off than anyone expected. You did not, in any way, help the human clan to get close enough to Dust monsters but as the only human on the payroll close to the Boss, the target on your head can be seen from miles around.

“I need a fucking cigarette,” you whine under your breath, slamming your fist into the handle of the door to the secluded alley behind the safehouse.

**Notes for the Chapter:**

> [the fire of my garbage blog is like the warning beacon of gondor (link to tumblr)](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  _offers you an awkward brofist_ don't leave me hanging plz


	6. The Smoke Break

Someone else had the same idea.

“I thought you were sleeping.”

Sans looks up from the cigarette turning to ash between his fingers to look at you. “tried to.”

“Never thought I’d see a day you can’t sleep,” you say, “since I’ve seen you take naps in the _weirdest_ fucking places.”

“shaddup.” There’s no heat to his tone, so you read it as an invitation.

You take a spot on the short bench behind him, resting your back against his for support. He leans back into you, and in the privacy of relative darkness and solitude, you let yourself deflate against him.

For the last three weeks trailing the group that eventually jumped you, you’d been isolated from the rest of your clan. It’s the longest stretch you’ve gone gone since joining the monsters on your own. At first, you’d relished in the solitude, the return to a purely unadulterated hunt, something you did constantly before declaring loyalties one way or the other. Blending into a crowd was something you’d mastered as a street urchin and the skill molded well into your duties working for Boss. This job was going to be something you would have eventually turned into a mole operation.

Now your entire cover is blown.

“what’d boss have ta say?”

You snort. “Enough. Guess he’s having trouble collecting info. Showed me the loot you nabbed to pin this on Moresby. He saw the sigil on my taser burns.”

Without having to ask, Sans offers a cigarette to you over his shoulder, already lit. You take it to your lips and hate that this is the closest your lips have gotten to his. How many times have you imagined how it would feel to have his fangs at your throat, on your back, marking the insides of your thighs? You take a shuddering breath, wincing and groaning as your bruised ribs protest.

You want to open up to him, tell him what’s on your mind and really bothering you. Now that your cover is so much garbage at the bottom of the chute, what will be your role in the mob now? How are you useful to them anymore? You’re a liability. As soon as you’re healed enough to move to another safe house-

“fuckin’ dirty cheatin’ bastards, the lot of ‘em.”

Sans’s growl interrupts your thoughts. You snort a laugh, hissing in pain again at the way that jostles you. “You’re one to talk, bone boy. Don’t think I didn’t see that blue magic just because I was bleeding out.

“should’ve blasted them,” Sans mutters.

Silence falls between you as you smoke. You watch the way it curls upwards, through the chain link roof of this tiny fenced in alcove off the main building, and track the path of an airplane flying high overhead.

The monster at your back is broader than you by a few handbreadths, a wonderful wall of ribs to lean against. Neither of you have your jackets on, avoiding making them smell like smoke, even if you could use the extra layer on this chilly night. You greedily soak up heat from every part of his body that rubs against yours. It’s a poor imitation of the intimacy you shared after he saved you, after Grillby healed you, but you figure now that you’re no longer on death’s doorstep, Sans would go back to his standoffish ways with you.

“Sans…”

“yeah, sweetheart?”

“You’re an idiot.”

The ribs and spine touching your back go rigid, and you can feel the rumble of a growl as he starts to pull away from you. You press back into him and grow bold enough to lean your head back against his shoulder.

“But thanks for comin’ to save me.”

That stops him from trying to push you off and stand up. “don’t mention it. was nothin’.”

“Like hell it wasn’t. You took on three humans with fucking magical fucking _tasers_.”

Sans is gritting his teeth now. “i’m serious, sweetheart. don’t. mention. It.”

“You’re serious? I thought you were Sans?”

You count a victory on your side when he barks out a laugh. His bony hand slaps against his femur. The way his back shakes against yours, the ridges of his spinal column grazing against you, hits a few of the scars and scabs on you back but you hide your discomfort from him.

“stars. you’re somethin’ else.”

Both of you sit and breathe, enjoying the night and each other’s company while you could. You lean to the side to watch another plane lazily fly overheard. It’s easy to let your mind wander when you sit quietly with Sans. It reminds you of the first few missions with him, testing your loyalty, and the contract connection with Boss. As you watch the plane above you wonder where it came from, or where it’s going. You wonder if you’ll ever get to fly away on one of those and never come back.

Who are you kidding? No matter how far you go, or where to, your sins will follow. And as much as you’ve fucked up, allowed yourself to get attacked and compromised, you’d never leave these people that were your strange, murderous family.

You just hope that devotion runs both ways.

**Notes for the Chapter:**

> [♪ ♫ ♬ come with me and we'll be in a world of tumblr garbage fires](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> **bros** You guys are the heckin best. HIGH FIVES ALL AROUND.


	7. The Man Who Came in from the Void

You’re trying to meditate in an empty office when Gaster finds you again.

“Hello, Sentinel.”

His voice is clicking far more than when you were downstairs in the bunker with him a few hours ago. You can practically smell the Void on his clothes. Boss must have sent his multidimensional brother on an errand. 

“Hmm. Hello, Gaster.”

“I do apologize for interrupting you, but the Boss sent me to you.”

“Of course,” you say. Your joints protest as you get up off the empty desk, and Gaster holds out a hand to steady you as you come down. “Thanks. Where does he need me?”

“The bunker.” Gaster’s hand is smooth bone in your warm and calloused one, the hole in his palm barely registering against your skin, since you can see through it but nothing passes through. “Would you like me to escort you?”

You smile. Besides Sans, this is your favorite skeleton brother, for good reason. He’s helped you immensely with concerns of the Soul. And is surprisingly canny in the ways of the heart for a man who spends more time staring into the Void than working on his relationships in this reality. You’re glad he fell through the Void to your universe.

“I would like that, please.” 

He cocks his head to the side and smiles a little, offering his arm. You know below the arms of his lab coat he is more Void than monster, but that’s never bothered you. There’s a piece of that darkness in you, too.

“You’re healing well, I see,” Gaster says as he leads you down office hallways towards the service elevator. “Grillby returned to Safe House 5, per the reports, so I do not doubt he will return here soon. There was another altercation on the northside of the city and his services were required.”

A heavy stone forms in the bottom of your stomach. “Did we lose anyone?”

Gaster’s skull tics from side to side. The top of your head comes to his shoulder, but he’s jerky enough right now that his head almost bumps into yours.

“Gaster.” You use your grip on his elbow to stop the two of you. “Breathe, please.”

The sharp intakes of breath that would indicate hyperventilation in a human start to calm him, bursts of clear and - relatively - clean oxygen filling his body. It doesn’t take long for him to regain composure. “I apologize. What did you ask me?”

You want to ask him why Boss sent him back into the Void but refrain. Gaster doesn’t like to talk about his time there. “What happened on the northside of the city?”

“Three monsters were ambushed, like you were,” the man from the Void explains. The two of you restart your trek to the elevators. Boss does not like to be kept waiting, but Gaster cannot sprint like you or Undyne can. “We managed to collect two of them, and the third is unaccounted for.”

“Fuck,” you hiss through your teeth. “Who were they?”

“Foot soldiers, as far as I overheard.”

His wording makes your mouth twitch, threatening a smile. “Taking peeks where you shouldn’t again, G?”

“Maybe I have, wiseguy. What is it to you?”

As the elevator doors slide shut you sputter out a chuckle. “Talking like them doesn’t suit you, G. I prefer the way you talk. The good, proper, and respectable Doctor W. D. Gaster.”

“Hmm. Thank you. Though I do not consider myself ‘good’.”

“You don’t give yourself enough credit.”

“And you give me far too much, Sentinel.”

Your conversation is abruptly ended as the elevator reaches the lowest level of the building. As one, you and Gaster parted from each other, always careful when exchanging physical affection between you. For one, your credibility as the cold knife in Boss’s back pocket depends on it, and it would not do for most of the family to know you could actually touch Gaster. 

Two touch starved individuals. The coldest knives in the family’s silver set, one openly coated in the Void, the other hiding that connection any way they can.

It’s good you parted before the doors did, since there are more than a dozen faces waiting for you when you arrive. Boss is flanked by Undyne and his brother, whose red irises are hidden behind mostly closed lids. He’s destroying toothpicks in record time, his smoking banned from this part of the safe house, the instruments too delicate for the pungent magical cigars he prefers. Undyne is standing at attention and staring at a map posted on the wall behind her, and you’re certain if you could see her face that you’d see her single eye scanning it at top speed. 

Several of the monsters present had blood on their sleeves, and their guns or preferred melee methods on full display. Ten months ago you’d have feared for your safety and used your ability to assess a room in a moment to escape, but now you stare at your comrades and try not to think of who could be missing of their number.

It hits you like a ton of bricks.

“Where are Guy and Asriel?”

**Notes for the Chapter:**

> [a portal to a new world ~~aka my tumblr~~](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> It's Saturday! It's been a week of daily updates! Wee!


	8. The Puppetmaster

“Asriel is in another safe house, not that it’s  _ your _ business,” says a tart voice.

The goat monster Toriel, the previous Senhora Dona of the Underground, sits in the corner your peripheral vision couldn’t pick up. So, the first unforeseen side effect of your attack. The damage to your vision hurts your pride more than the scars on your neck with the enemy’s sigil. If Sans hadn’t already obliterated your attackers you’d find whoever used a taser too close to your eye and would start by slowly plucking their fingernails out of their hands. 

As risky as it is to cross the woman, you dare. You always dare. “ _ Mia regina _ , what a pleasure. As always.”

The glass beaker in Toriel’s hands, lazily tossed from hand to hand as you spoke, shatters in her grip. Alphys squeaks in surprise and works to clear her face of a glare. At your elbow you can feel the pressure-filled presence of the oldest skeleton brother giving you a warning.

“SILENCE, SENTINEL. THAT’S ENOUGH OF YOUR GAB.”

“Yes, Boss.”

Boss levels his pupil-less gaze at you, his clawed hands drumming against his folded arms. He’s wearing an all-black suit with a small red pocket square the only break in planes of dark fabric. Everyone else is dressed similarly. 

There’s to be a raid.

Boss barks out orders to the assembled, his voice carrying the solemnity of the moment into everyone present. “THE MORESBY CLAN HAS SEEN FIT IN THE LAST TWELVE HOURS TO NOT ONLY ASSAULT THE SENTINEL BUT THREE MORE OF OUR FAMILY ON THE NORTHSIDE. THESE PROVOCATIONS WON’T STAND.”

“They will expect you to act, Papyrus.”

Your eye twitches at Toriel’s voice rising in the room again. No one calls the Boss by his first name, not since the last time his LV increased. Boss’s face snaps to her with violent intent written there.

“OF COURSE THEY WILL. AND THOUGH THEY THINK THEY’RE PREPARED FOR OUR ASSAULT, THEY ARE WRONG. DO YOU DOUBT ME, SENHORA DONA? OR HAVE YOU FORGOTTEN SO SOON WHO LEAD A SUCCESSFUL BRIGADE AGAINST YOU AND YOUR KING?”

As the only monster with higher EXP and LV than the Boss, Toriel still holds sway, but knows when her authority is out of line. She waves her hand to him, bowing her head slightly, the red lights of her eyes fading for a moment as she closes them in deference to her Don. You know that slight against her won’t go unpunished, but it’s unlikely Boss will receive the brunt of her ire. Woe to any humans crossing her path this night.

You recall Gaster’s one-time explanation of the dynamic between the former leader and the current one, a passage of power that had more to do with magic and skill than simple rank. Toriel had ruled the Underground with her King, Asgore, for centuries of their captivity. Violence, not unlike the life you lead today dictated the goings-on of that world, and you still didn’t believe a single small child inspired these monsters to cease long enough to work together and break the barrier. Knowing what you do of Boss, it feels much more believable he did what others were reluctant to do.

Kill the King, gain his EXP and increase his LV high enough to stand a chance absorbing a human soul without losing his mind, and breaking the barrier. The details elude you. But that’s not your job.

The dark shadow that lives inside you bubbles for attention, neglected for days now during your covert operations and however long you were knocked out from the assault. Damn, you  _ really _ wish Sans had managed to take one of them back here, too, so you could tear them apart. The crunch of bones beneath your knuckles would shut the Void up in an instant.

“THOSE ASSEMBLED ARE SWORN TO SECRECY. IS THAT UNDERSTOOD?”

You feel the tug on your contract as Boss pulls the strings. The way his fingers drum on his arm changes for a moment, and if you squint your eyes just right you can see the tethers that bind everyone in the room to him. Except...one monster. Startled, you blink your eyes fully open again and shout an affirmative back to Boss in sync with everyone else in the room.

“GOOD. IT’S BEEN CONFIRMED THAT THE FUCKING HUMANS ARE STILL CONSPIRING TO ACQUIRE ENOUGH POWER TO PUT US BACK UNDERGROUND.” Muttering fills the room until Boss makes a tugging motion with his hands, shutting everyone up. “BE SILENT! THERE IS MUCH AT STAKE. WE ACT AT DAWN.”

As Boss leans over the center table, tearing the map down from the wall as he does, he starts to point with his ridiculously long arms and dangerously sharp fingers at sectors of the city and assigning soldiers, captains, and underlings to each part to prepare to corner the Moresby’s once and for all. But through it all you’re having trouble focusing.

Why doesn’t Sans have a Soul contract with the Boss?

**Notes for the Chapter:**

> [hey. hey bud. you wanna see something cool? well you might find it here on my tumblr](https://uwa-so-frisk.tumblr.com/) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> guysguysguys I AM SUCH HAPPY VERY YES RIGHT NOW because there is _sobs_ fanart! [right here right now my jones bros](https://uwa-so-frisk.tumblr.com/post/169942082541/rainbow-sin-queen-mobfellsans-inspired-by-code) which means I got to add an art tag for the fic. EEEEEEEEEEE!


	9. The Card Shark

Grillby is still tending to the two monsters recovered from the incident on the north side so isn’t available to return to this safe house to check on you. You try not to let that bother you and don’t make another comment on it. Looking weak is the last thing you need right now.

You’ve heard stories about the monsters in your family being kind, peaceful, and harboring no ill will towards each other at one time. But those are just stories. Times like these demand different action. Living here on the Surface, it’s a good thing they decided to up their LV long ago, essentially facilitating their own slow genocide in the Underground. Those two underlings would have Dusted if not for that buffer of a few extra execution points. Monsters wouldn’t have stood a Snowdrake’s chance in hell against humans without levels of violence.

So, instead of another check up to see if your body is healing correctly, you’re standing in Sans’s room wrapping your hands and wrists to avoid breaking them when you throw punches later. The borrowed shirt is draped over the back of the single chair, your top half only covered by the loose fitting tank undershirt, so you have free movement to work out some of the kinks forming in your muscles. 

You also can see your new scars.

Sans isn’t a monster concerned with how he looks, unlike his brother who understands a Don’s image is half his power, so you’d had to nab a small mirror from another room on your way back upstairs. Your morbid curiosity spurs you to look at the marks of your failure. That, and the whispers against your Soul demand action. 

_ At least these are skin deep _ , you muse in your head.

The darkness inside you shudders in response. The irony isn’t lost on you, knowing what your Soul looks like. You do your best to ignore that pesky constant companion. Soon enough, the bloodlust will be satisfied, the cracks filled with the crimson sacrifice of another human who dares cross you or your family.

Now that you’re aware of it, with the other pains in your body subsiding in the wake of Grillby’s forceful healing magic, your left eye is doing it’s best to blind you with a headache. It sets your teeth on edge. When you close it, it doesn’t feel so bad. But you don’t have enough practice with an eyepatch to borrow one from Undyne for the rumble. You need to be firing on all cylinders.

Human Souls count for a lot of EXP, especially one like yours that already carries a LV in double digits. Upon death a Soul absorbs nearly all of the EXP of the Soul it vanquishes, like Boss had with the Bergentrückung when the ancient goat monster started to lose the plot.  What some of these monsters wouldn’t give for Boss to finally give the go-ahead to tear you apart. 

You are a wiseguy. An outsider. The Boss’s lapdog. You’d need another twenty years to gain more of their trust. And today it doesn’t feel like you have twenty  _ hours _ left at most. Even if you had time, you know some would still salivate behind your back.

Which is why you keep your cards close to your chest. And a few up your sleeve for good measure.

“figured you’d be here.”

You glance over your shoulder in the mirror to the door of the room. Sans stands there with his hands in his pockets, a hat pulled low over his face. The light from the hall illuminates his bones in a way that makes your throat feel tight and your pants tighter.

Taking your hands away from your neck, where you’d been inspecting the puckered flesh there, you turn to grab the shirt. Still doesn’t feel right to call it your shirt. Fuckin’ Felix, that beautiful bastard. 

“I can leave.”

“you can.”

The words sting, but you understand. It’s not the time to sit and drink and muse about your existence with the monster like you’d done in the past before a raid or rumble. You can feel the dynamic changed last night but you’d been hoping that...no, hope is for fools.

You’re already done up again, tucking in your shirt, when he crosses the room. The door shuts with a dull click, dowsing all light in the room except the single lamp next to you. The sound of his bones against the handle of the door are like throwing dice at a roulette table. Closing the distance between you in measured steps, his hand lifts, and your breathing halts.

“but you don’t hafta. ‘sides, you missed a button, sweetheart.” 

One of his hands, the claws mostly retracted, moves to slip a finger in the spot on your shirt where you’d missed a button in your haste. He takes in a sharp breath that hisses through his teeth. 

It’s like standing on the edge of a tall building, trusting someone to catch you with gravity magic before your body gives into the velocity, killing you before impact. You’re waiting for the signal to jump. The cue to keep moving the way inertia wants you to go…

Or do you fight it?

**Notes for the Chapter:**

> [~~definitely not a link to my tumblr where you can ask me anything you want nope~~](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  _drops a cliffhanger and runs awaaaaaaaaaay_ ♪~ ᕕ(ᐛ)ᕗ


	10. The Promise of a Good Time

**Summary for the Chapter:**

> let's earn that E rating shall we?

The back of Sans’s finger brushes against your stomach, the contact dulled by your undershirt, but you’re so focused on what he’s doing it feels like a shock. A breath passes through your lips slow and shuddering. Your eyes stare at the top of his head as he watches his fingers.

And still, you don’t move.

Sans twitches like he’s caught what he’s doing, and a faint red glow blooms below his hat. He’s barely shorter than you but it’s enough for him to hide his expression. Instead of dropping his hands away, they twitch again, and he fixes the buttons you missed, the edges of his claws grazing your stomach and chest again as he does.

When one of those claws brushes the place above your sternum, you lift your hand to grip his shoulder as you shudder. It’s a shock as powerful as the one that dropped you with that taser, just as debilitating, but not painful. 

Oh, no not painful  _ at all. _

“Jesus  _ fuck _ ,” you whine as he pulls his hand away, startled. 

The top of your shirt is still half undone from his work, so you both see the glow of your Soul straining towards the surface of your skin below your shirt. It’s less a color and more a feeling. When you’re finally able to open your eyes again, your hands are still gripped into his shoulders, your nails digging into the wings of his scapula, and he’s moved to press you against the cold metal door. 

Eye sockets dark and ravenous, Sans digs one hand into your hip and the other presses into your neck, fingers pressing into the sides and avoiding your windpipe. A power move. Forced submission. But is it forced if every part of you is willing this to happen?

“you get one chance t’say no, sweetheart.”

“Or what, Sans,” you choke out. The hands against you start to vibrate the more you move against him. “What will you do?” 

Your struggling isn’t to get away, it’s to get him to come closer. His body is still several inches away from yours. The only points of contact are his hands and it’s  _ not enough goddamnit. _ All it takes is your shoes to slip on the cheap carpet a bit and your legs surround one of his, but you stop short of rubbing yourself against his femur. This dance is familiar. You’ve even had other monsters in your bed, or in cars, as part of an assignment or not, but you approach this with eyes wide open. 

There is intent. There is danger.

And stars if this isn’t exactly what you were hoping to happen.

The skeleton rattles as he draws in a breath. Red irises, blown wider than you’ve ever seen them, rake across you and the feral grin widens with impish delight. He may be just  _ that much  _ shorter than you, but he is in control right now. 

And he knows it.

“it’s the difference b’tween a good time…” He pauses to slowly open his maw. The gold fang all but glows in the low light. “...and a  _ bad time _ .”

Your bluntly cut nails grip through his shirt, dragging at him. Without that grip and his hand at your throat you don’t know if you’d be standing.

“Then fucking show me a good time,  _ Red _ .”

That does it. His code name. You don’t own the string on his Soul, and you don’t know who does if it isn’t Boss, but using it with that level of intent is enough to shatter whatever vestiges are left of his resolve. The hand around your throat directs you to the bed, your arm flailing and knocking over the single light source in the room on the way. Neither of you acknowledge the shattered lamp on the ground, the acrid smell of a burst bulb. 

The hand that’s at your hip twists to grab one of your arms, pulling it up behind your back to pin you face down as the one at your neck move to fist your hair in its claws. Your legs are still free so you try to wrap them around one of his to gain some control back, but he’s too fast. Too strong.

“no ya don’t, sweetheart.”

You keep trying to draw him closer to you, to feel the bones against you that you can hear starting to rattle. But he isn’t giving quarter, taking his time keeping you pinned, just to show you he can. Though, you both know if you really wanted him to let you go that you could manage. Without warning, Sans uses his grip to flip you, and even with your hands scrabbling during the movement, he traps both hands into one of his. The claws, fully extended now that they aren’t running over the swell of your ass or gripping your hair, poke into the mattress beneath your wrists.

“so,” he says, huffing in a breath. His voice is rough; you practically feel it grate against your nerves. “you wan’ta good time with the monster, huh?”

You don’t have the breath to answer him with words, and buck your hips into his as you arch your back. “Stop. Fucking.  _ Talking. _ ”

“as you wish,  _ sentinel _ .”

**Notes for the Chapter:**

> [PLEASE TALK ~~YELL~~ AT ME HERE ON TUMBLR I LOVE IT](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> ┬┴┬┴┤ ͜ʖ ͡°) ├┬┴┬┴  
> hey how's it going?


	11. The Point of No Return

**Summary for the Chapter:**

> sin sin sin sin sin

Fire. There has to be fire in your veins, or ice, or some goddamned jumper cables straight to your Soul. Your hips buck in response to Sans’s voice, and they get brief contact with the monster holding you down.

You don’t realize you cried out until Sans’s hands holding your wrists down press harder, almost hard enough to bruise, and his fangs are inches from your mouth. His breath, something you still don’t understand the mechanics of, is hot on your neck. There’s a tang in it you recognize as nicotine and mustard. 

“you see how that feels, huh? usin’ a fuckin’ code name like that.”

The pressure recedes from your brain enough to form coherent words. “Again. Fucking say it again, Sans.”

“ah-ah,” Sans says, his tone admonishing and far too pleased with himself. A predator with prey between his paws. “shut your mouth and do as i say, sweetheart.”

You whine, again, moving your head to rub against his cheek. The grip on your wrists twitches a bit when you do, but doesn't loosen. Instead you feel his femur lift to grind almost painfully into your pelvis.

“i said, s’that clear?”

“Hhhnng- _ yes _ , yes!”

The teeth are closer to your neck, the side with the taser burns. They sting from the breath of the monster pinning you down. You can feel the way the teeth shift slightly when he speaks, never fully opening. He’s holding you down enough that you can struggle to get closer but it’s an effort. Your head is still swimming from the effect his use of your code name had on you.

“ _ yes what? _ ”

“Yes,  _ sir _ ,” you say, but unsure what he wants to hear your voice loses some of its conviction.

Sans grazes his fangs against your neck, the edges rough against the sensitive healing flesh, and you bite your lip to stop a whimper. 

“fuckin’ say it like you mean it, like you  _ want this _ .”

“Yes, SIR!”

You’re flipped over onto your stomach in the next breath, the grip on your wrists remaining as Sans tugs at your pants. You lift your hips to help him, a war in your head between hoping he gets them off faster and not wanting to destroy the only pair you have. In the end you hear a tear and just hope its repairable, or you’ll have to do a walk of shame back to Guy and Felix’s room.

A cool rush of air runs over the back of your thighs and your ass when your pants and underwear are dragged down. You realize one of Sans’s hands left your wrists when his claws cut thin lines into the soft flesh under the curve of your ass. You’re panting now, pressing yourself back to him.

“tha’s right,” Sans says. “present yourself to me like the good slut you are.”

You’ve been neutral before about this rough and dirty talk, since sex is commonly another way to do your job, but hearing from Sans makes you never want to hear those things from anyone else’s voice ever again. It will never be enough. The inflection is as reverential as it is demeaning, pooling heat between your thighs at a rate that is as thrilling as it is humiliating.

“when i leggo of your hands you grab the bars, you got it sweetheart? an’ don’t you fuckin’ dare let go.”

Moving your face to the side so you can speak, you reply, “Yes, sir.”

Your palms are sweaty against the steel bedposts, the pillow mangled from your mouth biting into it. Sans’s hands are not gentle in exploring the softest parts of you on full display. Each movement is precise, like he knows exactly what to do with your human body. You wonder if he’s ever been with a human before. You wonder how many. You wonder if he knows how many monsters and humans were here before him. 

You wonder if any of that even matters.

There isn’t much light in the room at all, so the increase in red magic behind you is easy to spot. Without Sans’s grip, your hands seek the cold metal of the head of the bed. You comply with his hands moving your body so you’re not kneeling over the edge of the bed anymore, instead your knees rest on the lumpy mattress.

All rational thought is chased away as first one, then two of his fingers press into your entrance. Biting into the pillow, your cries are muffled. You want to turn behind you to watch him, but you can’t with your arms above your head, your chest pressed almost flush to the mattress, and the only light source the glowing red of Sans’s magic.

“what did i say?” Sans growls. He noticed your squirming to try and turn, your grip slipping from sweat. You can feel his breath on your back and one of his fingers curls inside you. “don’t you fuckin’ let go of that bar.”

A little flicker of defiance rises in you that you squash. Yes, it would be fun to tease him back, but you need this. Stars, you’ve wanted this since you saw those stupid fucking skull shaped cufflinks in a pawn shop, scattered on the floor after you helped trash the place, grabbing them with a particular person in mind. You don’t want him to stop. You will comply.

“Yes, sir!”

“much better,  _ sentinel _ .”

Your cries of pleasure and the creaking of the shitty mattress beneath your shaking legs drown out the sound of footsteps passing outside the door.

**Notes for the Chapter:**

> [come feed my tumblr addiction](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> gooooooooood morrrrrrrrrrnnnnnnnnniiiiiiiiiinnnnnnnnnnnngggggggggggg


	12. The Consequence

**Summary for the Chapter:**

> siiiiiiiin is in

If you’d expected getting fucked by a literal skeleton to feel anything like any of your other experiences, you were dead wrong.

There are so many parts of him poking into you in the least comfortable places, and his claws search out any bit of your soft flesh he can to sink into. You are certain you’ll have a walk of shame to get more borrowed clothes. 

Sans’s hips connect with yours behind you as his cock slams into you over and over again. Flesh against bone is a uniquely violent sound, multiplied by the force he’s putting into every movement. You want to see what’s rutting into you, to see how he works. There is absolutely no question that that is a cock of some kind filling you. But, he’s giving no quarter on his grip. And, when you’d so much as jerked in a way that loosened your grip on the bedposts, he’d slipped out of you and bit down on your neck in punishment faster than you thought possible. 

There’s a rush of cold against your neck where you expected warmth. Everything else about him is warm, near scalding hot in some places, but the feeling of his mouth against your neck is colder than the muzzle of a gun in a snowstorm. The disparate temperatures in your body send spikes of pleasure from your head to your toes.

“told ya not to fuckin’ let go,” Sans growls into you as his teeth brush the edges of your wounds. You can see his face and some of his teeth in the corner of your eye, but you feel his mandible reaching all the way around to graze your spine and the other side of your neck. 

If you had any doubts you were with a monster this sight would chase them away.

Each time his teeth graze against your neck, with every beat of your heart pushing the thin skin closer to those razor edges, your breath catches in your throat. You want to play this game to completion but your body is a screaming mess demanding that you speak up.

“Stop -  _ huff -  _ fucking talking and -  _ hnnng - _ fuck me, you son of a bitch!”

Sans’s teeth puncture your wounds in a quick snap before he backs off again. There’s no blood, to your surprise given that he just bit you close to your jugular. There is only the glow of red magic left behind. The words flowing from Sans’s mouth are more guttural warnings of harm as he grips your hips again. 

There is no mercy in his pace, leaning his weight into you until your knees give out and he’s pinning you down completely. The added pressure and change of angle is what you needed to press your most sensitive parts against him and you clench around him as you come. 

It’s at once bliss and torture, as his demanding thrusts don’t let up as your body grows oversensitized. The rough fabric of his pants pushed down to his knees rubs against the little nicks and scrapes he made with his claws earlier on your thighs. Tears fill your eyes at the stimulation. You don’t know how much more you can take, but you’ll gladly push yourself as far as you can if it means another moment with him.

He doesn’t give you a warning before he’s cumming into you. The feeling is warm, warmer than the feeling of his chest pressing against your back. With him on top of you like this, you start to understand why he would not allow you to turn to look at him, no matter how much you wanted to. Monster Souls during heat or sex are vulnerable, doubly so with a partner where more is at stake than chasing an orgasm. You force yourself to stop thinking about that.

Hope is for fools.

The rattle of his bones as he puts his clothes back together is loud in the silence that follows your fervid fucking. He lands heavily in the chair across the room from you, and you mourn the loss of his touch like a starving man staring at a feast. You’re barely able to catch your breath and turn over, pants pushed down around your ankles, before Sans is able to hide the flame of his Soul beneath his chest. That gossamer thin tether you saw in the bunker earlier is back, and brighter than ever. 

And it makes a beeline directly to you.

**Notes for the Chapter:**

> [1-800-spendstoomuchtimeontumblr](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> HELLLOOOO ALL YOU _BEAUTIFUL_ PEOPLE OUT THERE!
> 
> So for all you sinners out there I have a Mafia rec. It's a Fell!Sans, too! I haven't had a chance to read past chapter 2 so far, but it's a collection of...sin. Just lovely sin of the 'monster heat' variety. Chapter 2 in particular _might_ be something you're into. Make sure to check the author's tags and notes, but it's another Mobfell!Sans for your reading pleasure.
> 
> [Heat-tale](https://archiveofourown.org/works/8140172/chapters/18657806) by [Dark_Crystal_Demon](https://archiveofourown.org/users/Dark_Crystal_Demon/pseuds/Dark_Crystal_Demon)
> 
> **also if there is anything you are curious about in this fic, i am only five chapters ahead, so your comments could affect the outcome of the plot**


	13. The Cost of Transgression

**Summary for the Chapter:**

> Your actions have a ripple effect.

“The biodiversity of the last universe I drew from was under par. Please note that my travels during the hours of 21:00 and 22:00 have been the least fruitful.”

“Yes, um, okay. Uh, were there any other hours that had issues, Dr. Gaster?”

Gaster rubs the crack beneath his left eye pensively, the bone against bone sound filling the lab with an unsettling scraping that sets the younger doctor’s teeth on edge. Alphys really wishes he wouldn’t do that, but if it stops his ticking, then she could manage to listen to it for a few minutes.

The room stinks of the Void, a feral and oppressive scent that sticks to her clothes. She will make sure to change before leaving the room and meeting with Undyne. From what she gathered of the meeting earlier, the woman will be leading a charge in a dangerous raid, and Dr. Alphys is afraid that...no, don’t think that way.

“Dr. Alphys, did you record the last few moments of my report?”

Dr. Alphys starts with a jerk big enough to knock the clipboard from her hands. “Oh, oh my goodness, I’m sorry, it’s just-”

“Stop,” Gaster says with a sigh. 

It’s curt and stings her feelings more than she cares for. Dr. Gaster is kind and soft-spoken most of the time, so she tries to focus on that instead of how he is after his trespasses in the name of science. Maybe she  _ should _ take Undyne’s advice and raise her LV, and maybe that would get rid of her stupid stutter and easily jarred nerves once and for all. 

“I’m sorry,” she says, picking up her clipboard, and sliding into the stool across from her mentor. “R-repeat that, please.”

Gaster’s thousand yard stare feels like staring into the river at night, hundreds of feet below her as she walks across the bridge. No, stop it, that was years ago, don’t think about that. Undyne says dwelling on that won’t make the memory go away any faster. Still, she feels the slip of cold ocean air beneath her jacket, and the gaping maw of darkness ending in the slow churn of dark water below her feet…

“Dr. Alphys if you cannot focus on this meeting then I will be forced to ask you to vacate this room.”

Leaning over her, Gaster uses his formidable height to bow almost in half over her smaller frame, his skull ticking in a syncopated rhythm.

“The Void-” she starts to say, but his fist slams down on the steel-topped table loud enough to hurt her ears.

“Leave. Return when you can perform your duties.”

Her tail disappears around the lip of the door faster than a rat fleeing a flame.

Once she’s gone, Gaster sinks back down into his stool, elbows resting on the table and head in his hands, trying to stop his skull from trying to yank itself back into the Void. He resumes the gentle stroking of his first time wound and closes his eye sockets. Focusing his breathing, quick and sharp intakes of breath, he can feel the pressure recede, and he can think again.

Dr. Alphys knows better than to be in his presence without her wits about her after a journey through the Void. Everything about his person is cloaked in the all encompassing pressure of a place no thing of flesh or bone or magic should ever go. The Void is just what it’s name implies, an absence, and it takes all his focus to keep himself together in the literal sense when trespassing through it. Once he’s back out in reality, it tries to tear him apart before he can take stock of what he learned. Things from the Void are not supposed to be. His memory of that realm is a sieve as soon as he leaves. He’d rather not tell anyone about what he sees there but the little assistant is more useful than she thinks.

He knows what the other monsters call him behind their hands when they think he can’t hear them. Voidster. The name makes him chuckle when alone in his lab. The citizens of monsterkind took after their Bergentrückung more than they wanted to admit. It’s not the cleverest title. Too on the nose for a race that seldomly has typical noses to begin with.

Holding his head, he can feel the way his neck strains against every tic, every jerky movement, until the movement of his thumb against his wound calms him enough to stand and grab his mug of tea. Each step is like walking through fire as his joints try to bend ways they aren’t meant to. But he manages. He always does. He must.

On his walk towards his wooden workbench, his skull violently and without warning tics to the left, pulling him down to the floor with it. There’s a tug at his Soul that drags him. No, not his Soul. The Void drags him down. Knees first, he lands on the cold concrete and isn’t able to catch himself before his head falls, too, with a sickening crack echoing in the lab no one would likely return to for hours.

**Notes for the Chapter:**

> [tumblr is still cool right?](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Oh nooooooo another cliffhangerrrrrrrrr whatever shall we dooooooooooooo. 
> 
> (also the amount of people who are hating on this fic's version of Toriel kind of gives me life btw)


	14. The Die is Cast

The last hour is a blur.

Sans would not speak after your tryst, and you refuse to be the one to break the silence. You know Soulfire is the thing to blame for what happened between you but you wouldn’t change a thing. All the feeling did was jumpstart what you felt was inevitable anyway. If Soulfire was the only way to get Sans to respond to your little indications of attraction, so be it.

The heady feeling of your near death experience at your back and the planned raid on the Moresby’s had pushed you into thoughts of desperation and desire. When his hand brushed your skin above your Soul, you both were done for.

Everything with monsters is intent. If he didn’t want you even half as badly as you want him, the spark would not have happened.

You just wish you didn’t feel as though Sans regrets it.

No matter. You try to convince yourself to push those feelings away. There’s work to be done.

Your clothes are changed again, and if others notice you’re dressed differently, it doesn’t stand out. Monsters of all shapes and sizes congregate in the garage on the ground floor of the safehouse. If they don’t hold a weapon, you can feel their Souls alight with sleep bonuses or a little more EXP than they had earlier that same day. The river would boast a new batch of bodies at the bottom this night.

There’s an ache between your thighs and heaviness in your Soul you can’t shake. No matter how many steps you take away from that room, from Sans, you can feel the pull. You know you don’t regret the Soulfire, but you suspect it’s that little red thread you could see tying your Soul to his that’s calling you back to him.

Damn it. You need to see Gaster but there isn’t the  _ time _ . 

Like you warned Boss earlier in the evening, there is not enough time to dally. If your cover was blown then it’s likely there is a spy or the rival family is close enough to their goal to be reckless. To stop and try to figure out what kind of bond was blooming between yours and Sans’s Soul, and why it waited until now of all moments to surface, would be selfish and stupid.

“THE CANINE UNIT HAS ALREADY SCOUTED THE AREA WHERE ASRIEL, GUY, AND AARON WERE ATTACKED.” Boss’s voice booms over the crowd. Everyone’s attention is on him the moment he opens his mouth. “THERE ARE NO INDICATIONS OF A SECOND ASSAULT IN THIS REGION. OR ON THE DOCKS WHERE OUR SENTINEL WAS ATTACKED.”

Some rumbles and murmurs roll through the crowd. Stars, there have to be three dozen monsters filling the tiny space. It reeks of magic. Individually the scent of a monster’s magic doesn't bother you, but like this it’s as if you’re shoving your nose into a perfume display in a department store. Far too much information to sift through at once. 

Most of the monsters are already grouped the way Boss ordered in the bunker turned war room. He’ll need to fill you in on the way of what he needed of you. Typically he sent you on your own, but now that you’re known as the monster’s human, well...you suspect you’ll be sticking closer to the group this time.

You stay on the stairs, hunkering down to make yourself near invisible, but it’s impossible. You’ve already been spotted.

Boss tugs on your bond with a jerk of his hand in his pocket. An observer could mistake it for a twitch of the hand playing with some keys in his pocket, but you know better. The moment he said your code name again you could feel the leash tighten. Without hesitation, you obey, but make a small show of taking your time to wind through the crowd. The tug feels more automatic than truly commanding, though you don’t take the time to consider the implications of that yet. And you  _ definitely _ don’t compare the feeling of Sans saying your code name instead of Boss. 

The ache in your thighs gets a little stronger.

Undyne is notably missing when you go to stand near Boss, Toriel on his other side instead. Boss’s second in command must be with the canine unit. 

You’ve only seen the Senhora Dona move into direct combat once before. Only a threat to her son could move that mountain of a woman.

“THERE WILL BE NO RECKLESS ANTICS TONIGHT. MOST OF YOU CARRY THE HIGHEST LV IN THE FAMILY, WHICH IS WHY I HAVE ASKED YOU HERE TONIGHT. DR. GASTER HAS PREPARED A SESSION FOR EACH OF YOU THAT GAIN SIGNIFICANT LV, AND ANY WHO RESIST INSPECTION WILL BE ABSORBED.”

Absorbed. The almost kind warning of friendly execution. A monster that gained too many LV too quickly could lose their mind. 

Everyone remembers the Bergentrückung before Boss removed him.

“And if you do not heed this warning,” Toriel adds, “I will not hesitate to act on the field myself.”

Mutters of “Yes, Senhora Dona” filter through the crowd, the same level of deference presented to Boss given to the former Queen.

The rumble of a dozen cars starting up fills the air outside the garage. Tension that tastes like bitter coffee fills the air: strong, fortifying, and all-encompassing.

Time has run out.

**Notes for the Chapter:**

> [every day i'm tumbling](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Geez Sans, what gives?
> 
> What are you guys up to this Saturday?


	15. The Eye of the Storm

The press of Sans’s thigh against yours in the backseat of the car is torturous.

No one speaks, the skeleton brothers both preoccupied in their own way. Boss finished explaining what you expected to hear, that you were to stick by his side the entire night, for your protection and his. Your health hadn’t been evaluated since Grillby left for Safe House 5, and you were still unconscious then. The damage to your eye remained your secret but you had a feeling Boss knew just by looking at you that, while your healing is nothing short of miraculous, you are not in top form. 

You hate it. At least he doesn’t look at you in pity, or like you’re a liability. He looks at you like he always has: as a tool he knows how to wield. You’re determined to be an asset and not a nuisance tonight. If guarding Boss is how you do that, so be it. 

Even if it means working this closely with Sans.

He’s sleeping. Of course he is. You let yourself be frustrated with him even as you let him sleep. He needs the health bonus. As strong as he is -  _ especially when he’s pinning you down into a mattress  _ \- Sans does not have a very high HP. 

Each increase in LV should increase a monster or human’s HP as well as their power, and you haven’t known Sans long enough to understand how that works for him individually, but you do know that for the LV he carries he should have a much higher HP. One stray bullet hitting him just the wrong way and he’d Dust. 

There is no way you’re letting that happen. Not tonight. Not ever. Not until you get some fucking answers about this Soul thread, this strange contract between you.

You’ve tried to push the memory of the Soulfire incident out of your head so you can focus, but it isn’t working. You can still feel the weight of his code name on your tongue. Boss has said yours plenty of times, and that is  _ not _ the same reaction, not at all. What does it mean? To try and distract yourself, you watch out the same window Boss gazes out of. 

It doesn’t work, so you resign yourself to inconvenient images of red glowing magic, white bone holding your hands above your head, and a silk-thin line connecting your Soul to his.

Was the thread always there? You don’t think so. After your first session with Gaster to assess your LV before joining the family officially, you noticed a change in your vision. The change occurred gradually, but when you noticed it the difference was staggering.

Boss insisted the first time you came to him to not only see but to touch your Soul. At the time you didn’t understand the full implication of the action of physically touching another’s Soul, but you understood this was no small request. More demand than request, you did not refuse for fear of instant absorption. You could see the hungry way every monster stared at you on the way to the Boss. 

The moment was more than intimate, it was all-encompassing. You knew monsters had a way to see through a person’s lies surer than the polygraph, but never imagined that was what they did, literally look into a person’s Soul to read their intentions.

Sans was in the room that day, too. When you’d asked him why, he’d hedged and explained it was for Boss’s protection. You didn’t believe him then and you wouldn’t believe him now.

Each time the car passes over a bump or pothole, Sans’s head knocks against the window beside him with a dull thunk. His hands are shoved into his pockets. You wish you could sleep now, too, and escape reality for a moment or two.

The tightness in your chest has nothing to do with your healing ribs when you look at him. The man is a puzzle, an enigma. 

You feel the weight of eyes on you, and turn to meet Boss’s gaze. He’s turned his gaze to peer at you instead of the passing street lamps outside, and the steady increase and decrease of light behind him sets a striking image. You don’t back down, meeting him gaze for gaze. It’s obvious he caught you staring at his brother.

“NO MORE ERRORS, SENTINEL,” Boss says. His voice fills the cramped space and you’re amazed it doesn’t wake Sans. 

“No, sir.” Your voice is quiet and strong.

“HOW ARE YOU FEELING? HAS YOUR BODY MENDED?”

His concern almost makes you smile, the tone removing a tiny piece of concern from your Soul regarding your fate with the monsters. But you won’t allow yourself to let your guard down.

“I’m well enough, Boss. I won’t let you down again.”

“OF COURSE NOT. I, THE GREAT AND TERRIBLE PAPYRUS, EXPECT NOTHING LESS.”

“Of course, Boss.”

You don’t bother hiding the way you gaze at Sans now that you’ve been caught. The dawn threatens to claw its way over the lip of the ocean in the distance, coloring the harbor by the road in brilliant hues. It makes you want to hope you’ll survive another, but you know better.

Never forget: hope is for fools.

**Notes for the Chapter:**

> [tumblr is my city is my town](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Reader u so dramatic


	16. The Mundane Ambuscade

Gravel crunches under the tires of the car as it pulls to a slow stop. You can hear the other vehicles powering down around you, the soft hum of the electric and magical engines barely perceptible when they’re on. Without that hum, though, the silence presses against your eardrums near violently.

Your group is the first to leave their car. Boss steps out, all legs first, and as you wait for him to move you can feel Sans stir behind you. There’s a ghost of a bone finger running along your arm for a moment before you’re outside. It’s gone before you can see the white of his hand against the black of your sleeve.

You can’t let yourself put any emotional weight to that touch.

Streetlamps up and down the block are out, switched off automatically since the dawn is peeking over the horizon. The brick buildings around you block out most of the light, large strips of gold cast across alleyways instead. 

Was it only last night you stood in an alley like this, the sun almost set in the distance, when the ones you thought you were tailing jumped you? You remember the scuffle of feet that gave them away as one slipped on an oil slick left behind by an outdated truck. The scent of sea air fills your lungs for a moment as a gust of wind flows through the space, bringing you back to that moment of blood.

Boss buttons up his jacket, a flash of a pistol barely visible beneath it before he smooths everything in place again. No one is speaking, and you can barely hear the group’s collective breathing. This is the oldest part of the city, a part where almost no one lives anymore, and is the place the clans have always met to settle disputes in the open. The monsters all look to Boss to get their next orders, and since you’re standing just next to him, you feel the weight of their gazes on you as well. You want to duck back into the shadows, where you belong, but you stand your ground.

There’s no movement for the space of three breaths before the first shot is fired.

Chaos. Movement everywhere as you feel the tug of a shortcut yank you through the Void with Boss right there with you. Sans’s hand on your arm is rough, desperate, and the trip through the Void leaves you with a keening sense of loss. 

_ Soon, _ you promise the mark inside you.  _ Soon. _

It requires blood, and blood you shall give. 

As much bullshit as you went through the last day, you still have a handle on who you are under everything, under the worries about your worth to the family and whatever the fuck is happening between you and the shorter skeleton at your back. You are a ruthless killer that takes risks that have huge payoffs. Now is no different. You’re here to protect Boss, but you will not allow these fucking trash humans to nab one of your family, or get any closer to locking them away again.

Your elbows hit the edge of the rooftop as you lay yourself flat. It’s not the best vantage point but it’s better than standing in the middle of everything on the ground. After such a series of dirty tricks on the human’s side, the monsters are going balls to the wall with their magic. Governmental bans be damned.

No one is holding back. A turquoise spear blips into existence as you line up your first shot, leaving Undyne’s hand in a deadly arc towards a sniper or fighter you can’t see from your angle. The man who had a club raised behind her back is the first person you kill tonight. You know she notices your action by the jerk of her shoulder before she is off to engage another person, but there isn’t time for a heartfelt nod of thanks. 

The pain in your left eye increases as the dead asshole’s EXP makes a beeline for your Soul. Absorbing it is never without a sense of discomfort, of wrongness in your bones, but the Void crows in delight. Any amount of power it can absorb satiates it’s black hole nature long enough to stop chattering in your brain, drunk for a moment on the feeling of death.

You squint your eyes slightly, following the trails of magic easier, searching out humans to knock off easily. 

_ Pow. _ The fucker trying to choke Aaron out is down. 

_ Crack _ . No more baseball bat wielding scrub.

You’re out of bullets quickly, expecting more hand to hand combat, and when you rise from your position to reach into your pocket for another few rounds, you see the skeleton brothers in their glory.

Boss is crouched like a gargoyle over the edge of the building, holding onto the edge with one clawed hand while the other calls scores of bones up from the ground in waves, rising and falling to tear away the HP of the humans below.

“PATIENCE!” he yells, calling a battalion of light blue femur-shaped missiles out of thin air. The monsters he’s acting for instantly freeze, the humans around them dropping to clutch at magically-made wounds, some dropping entirely.

Boss is going to gain another LV today. You can feel it.

On your other side, Sans stands with one socket devoid of light, the other sparking with a blaze of fiery magic as bright as peering into the early sun’s rays. One hand rests in his pocket as the other lifts and spirals in movements too quick for your mundane eyes to watch, even squinted slightly, the smile on his face feral. Hungry.

Deadly.

**Notes for the Chapter:**

> [wazzzaaa tumblr link here](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> oooooooooooooooooooooh the Void is being a spookster.
> 
> I'm opening my ask box on tumblr for characters from this story. Any of them! Just let me know by sending an ask on tumblr which is linked above, anonymous or otherwise, and let me know who you're wanting to talk to. Any and all questions are welcome, even characters we haven't seen yet.


	17. The Aftermath

**Summary for the Chapter:**

> Shit got real and stayed real

_ Crack! _

Another bullet leaves your gun with a flash and kickback from the powerful weapon. Bullets imbued with yellow magic rarely miss.

Red and light cyan blue magic flashes out of the corner of your damaged eye, your left eye, as the brothers hold their own. You’ve only seen one monster get Dusted so far and your Soul crows with the thrill of battle. You didn’t know them well, you can barely think of their name, but you know it was one of Guy’s cousins. The fool was hopped up on too much EXP too quickly and grief over his missing cousin. Guy is your friend, too, but you know better than to run at a human with an electrically charged baton.

No, not electricity. That’s fucking purple Soul magic.

The noise is sure to have attracted attention in the surrounding area by now, but the police take their time around here when they know who’s involved. A runner likely left a message for them about this morning. It doesn’t soothe your nerves. You hate the police but you also don’t want to have to kill them. The family’s mansion is already compromised by those fuckers, the last thing you need is more monsters taken into custody and off the streets.

When the last human standing falls to their knees in front of Undyne, one of her spears skewered through his chest, silence falls over the crowd. A handful of the dozen monsters present are panting with the effort of keeping their Souls together, to absorb the EXP instead of letting it send them into further frenzy. 

Gaster would be busy Voiding Souls today. 

You hear Boss stand, his hands scraping along the concrete like nails on a chalkboard. Sans is crouched next to him, both eyelights back and scanning the landscape frantically. If he had hackles, they’d be raised.

Without breaking the silence, Boss looks to Sans and rests a hand on his shoulder. All the monsters on the ground watching you three unwaveringly. Sans doesn’t look up, just reaches over to grab both of you and take you through the Void to the ground with the others. He stays crouched and backs away once Boss lets go of him. You want to go to him but keep a hold on yourself. It is not the time.

Boss points the groups back to the cars, keeping quiet. The calls of gulls overhead slowly returns after the firefight. You feel your lip curl in a sick smile as you think how much evidence will be picked away by the rats with wings before authorities arrive, at least on the bodies that aren’t disposed of otherwise. Human death is so messy, but there is a haze of satisfaction in the air that tastes like copper, salt water, and singed clothes. 

Monsters on the brink of gaining an LV they cannot mentally or magically handle are escorted away immediately, ten of the vehicles tearing away in a spray of gravel, their electric and magical engines nearly silent otherwise. 

Only a handful of the family remain. The entire scene, from arriving to now, has only taken maybe three minutes. The barrel of your gun is still warm after firing so many rounds. You carefully holster it so it won’t burn a hole in your clothes and wait for your next order.

Your group moves out of the light of the sun into the relative shadow of the brick building you were just standing atop of. The windows at this level are boarded up, and you can see bullet holes in the plywood that seem fresh and others that have hints of decay around them, the splintered wood unable to hold up against the humid sea air. Boss directs you and the few others to an alcove with a set of stairs behind you. An easy escape you know well, since the stairs lead to a series of basements that eventually connect to a tunnel system created alongside the sewers meant for utility workers. 

“They anticipated us,” Toriel says quietly. 

She’s wiping the blade of her kitchen knife on a rag that looks like it was ripped from a dead man’s shirt. It likely was. The former Dona’s action reminds you she’s out here for her son, out to get the ones who threatened his life.

Boss scowls at her, and drops his voice a little as he says, “Of course they did, we sent runners, you fool. They showed their hand. They acted without the proper rules of engagement, which I also expected. The humans are lifting their LVs too quickly without a method to confiscate the unnecessary EXP.”

You shiver at the mention of Gaster’s true role in the family. Many others in the group do, too, you notice, from the uncomfortable memory of pieces of hard earned EXP drained from the Soul to keep the mental and physical and magical in balance. Even now you can feel it humming under your skin, settling and adjusting to its new home. As a human you can carry a heavier amount without consequence, but its a near thing. 

The Void within you is finally silent, drunk on death.

“As much as I would enjoy ripping your EXP from your Dust, Senhora, I have more pressing matters than your continued insubordination.”

Oh, you want to crow with adoration for Boss. The look on Toriel’s face would be the cream in your coffee for weeks. Each person present can feel her disdain and anger resonate off of her. Her lip curls to show some of her sharp teeth, and the dark red of her eyes burns with hell’s fury.

You get a moment’s warning before Toriel lunges.

**Notes for the Chapter:**

> [tumblr tumblr tumblr](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Uh oh what's gonna happennnnnnnnn??????????? Where are they getting purple Soul magic for those damn batons?????? Where are Guy and Asriel???? WILL SANS AND READER GET OFF THEIR EMOTIONAL HIGH HORSES?
> 
> All this and more in future updates.


	18. The Grasp of the Parallels

**Field Report A-24-JB487**

Fourteenth of April | Universe MF-3 | YR 2042 | 0840

_ Thirty one monsters and one human engaged in a ‘rumble’ this morning at dawn, close to 0600 hours. Returned to Safe House 5 before 0730. One monster Dusted during combat with Moresby clan and Dust collected to present to family to do as the individual wished. Monster tag is R-567D. In total fifteen humans with LVs above double digits were eliminated and another twenty lower than 10.  _

_ Make sure to notify Doctor Alphys the new yellow magic infused bullets were successful according to preliminary reports. It is still odd to consider ‘bullet’ has a different definition in this universe than my own, _

_ Siphoning commenced at 0745. V absorbed the excess EXP easily and has been sated. I do not doubt it will be brimming with the power of SOUL over the next few hours. There are too many whispers within pleading with me to step back in for the bloodshed to truly be over, however. I worry for the family. The humans are up to something that even I cannot see. _

_ All seven monsters close to over-absorption are now mitigated. The others will naturally absorb this EXP in the next few hours and gain an LV within their predetermined psychiatric threshold. No monsters show signs of Haze. _

_ At this time the Boss and a small contingent of monsters, plus SENTINEL, have not returned. Filtered reports provide intel they are headed to the Safe House holding the Crown Prince and Guy, the two monsters mentioned in FR A-24-JB484. Safe House number unknown. The third is still unaccounted for. At this time the identity of the monster is unclear, though I do not know if that is intentionally being kept quiet or is truly unknown. _

Gaster pauses his note-taking to rub the side of his head. If skeleton monsters could bruise, he would have a hell of one above his left eye. Of course it had to be his left one. He runs his index finger along the groove beneath it and tries to ignore the throbbing headache. 

The Void was most persistent after his last traipse through it, and he was unsure why. Several occurrences are recorded in his field journals related to the nothingness acting more aggressively, though that usually was after a truly wrenching tear, and there were no other signs of one. Except for his tumble. 

His skull tics to the side just to spite him for thinking on it.

During the sessions with the monsters fighting Haze, the EXP sickness that takes a monster without the strength to withstand it, his assistant was in and out. He can still smell her distress and he knows it’s related to Universe MF-3’s version of Undyne. No matter how many times he sees these two, they are the same. Dancing around each other and what their Souls desire until the anomaly -

No. Do not think on them. The Void is still present and it would be dangerous to call another human through by mistake. He still mourns the loss of those Universes.

Sentinel is the one he should be concerned with. Who could predict one human could have so much impact on so many different ‘verses, without a copy of them appearing in any except his own? The other one shows up no matter what, and is usually so close to Sans. Now that they are in his head he is surprised he has not seen Fri-

No! Do  _ not _ think on them. That only spells trouble.

Gaster returns to writing his report.

His mind drifts as his hands click rapidly over the keyboard. For a world further in the future than the others he has spent time in, this one is woefully disparate in terms of technology. It is...what is the word in human texts? Steampunk? 

Whatever the phrase, the introduction of magic much earlier in the human timeline created interesting advancements in some fields and woeful lacks in others. He has seen odder results of timeline interceptions, has even caused a few himself with and without meaning to. He is reminded of the brief glance he stole into human history in his original timeline to a moment of untold bloodshed. He can conjure the image of a the first few ‘aeroplanes’ used for combat. The sounds they make are nothing like the sleek jets of this plane.

The pun surprises him, and he chuckles aloud. This Sans...ah, he loves them as well, though he is more careful with them. With the way that younger brother of his withstands new notches of LV in his belt, Gaster is not surprised. Boss does not appreciate puns. His Papyrus - well, his ‘verse’s Papyrus - would never consider  _ hurting _ his brother over them. The Boss of this ‘verse, however, he would not put it past him. And Sans’s HP is always so low..such a troubling conundrum for him, especially here where his LV should have produced results on that front.

He wishes he could share the joke with the skeleton he grew up with, or even the one of this universe.

It is something he has never enjoyed about these universes, the ones where monsters take a turn towards violence. Truth be told, his Soul misses Sans, his confidant, his assistant, his family. But his own comfort is not worth the prizes of the universe, the ones yet to be. He sighs and puts his head in his hands, willing the headache to go away. He is frustrated and the answer to this universe’s puzzle can’t come soon enough. He wants to leave this forsaken place behind him for good. And one thing above all else rises the throbbing in his skull:

He does not know what will happen if he feeds more violence from this world to the Void.

**Notes for the Chapter:**

> [one day i'll get stuck thinking of a clever way to say this is a link to my tumblr but today is not that day](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Gaster, whatcha doin, messin with timelines n shit? No? 
> 
>  
> 
> **L i a r.**


	19. The Bone Tussle

**Summary for the Chapter:**

> Not as sexy as it sounds.

The angry magic under Toriel’s skin tries to burn your hands away as you grasp her wrists, the knife in her hands inches from your face. She’d lunged for Boss with deadly intent and your soul contract moved your hand. Not that you want to see Toriel attack Boss, you just recognize there is  _ no way _ you’d have been able to move fast enough or keep a grip on her without that added nudge of power and intent.

Some days you forget the way each monster has their own affinity, usually elemental, and the Senhora Dona reminds you violently that hers is fire.

Her maw opens with a snarl. The first blast of heat sears against your skin enough to create a shining burn on your forehead, the fur beneath your hands rising in temperature to match. You cry out in pain but it stops before moving from first to second degree burns. Your hands feel hot, like you’d laid them on the hood of a car in the middle of a summer day, but no damage there.

Sans stands between you. Though she is still struggling to reach you, there is a dark blue smudge in the center of her chest where you know her Soul lies, and it keeps her rooted.

You’re standing still with your hands curled in front of you, the shock of the burn wearing off after a moment, and your gun is in your hands the next. There’s a dark red bead of sweat trickling down Sans’s skull. 

“c’mon, senhora dona.” His voice is strained, and forcibly calm. “you don’ wanna do that.”

Without needing to look you know one of Sans’s eye lights is out, the flume of red from the other rising and dissipating into the morning sunlight. Of all the monsters present you know his approach is the gentlest with the crazed monster, and it hurts you to see the way he treats her with respect, reminding you of the connection the two of them used to have.

Most of the other monsters are crouched or ready to act, but are staying back. You can feel the high vibrations in the air from tension and conflicting loyalties. Damn the Boss for not absorbing Toriel before. This smells like trouble and you’re bound by your contract to Boss to do what he thinks is right.

“TORIEL IF YOU DO NOT CEASE I WILL ABSORB YOU MYSELF NOW.”

Boss’s voice echoes around the cramped space, cutting thought Toriel’s grunts of exertion against Sans’s gravity magic. Her knees sink further to the ground until she is on all fours. Her claws, stained a chalky brown from dried human blood, dig furrows into the dirt beneath her.

“Do it, then, you  _ coward _ ,” she snarls. “Empty threats from an empty headed  _ fool _ have never scared me!”

“YOU CALL ME, PAPYRUS THE GREAT AND TERRIBLE, A COWARD? A FOOL? THE ONLY FOOL WHO DOES NOT RECOGNIZE THE STRUGGLE OF HER OWN SOUL IS YOU.”

Toriel spits a dark glob of spittle at Boss’s feet, and you can see another collection of sweat appear on Sans’s head. He is holding onto her, but barely. You wish he wouldn’t. You wish he would let go so you can see what these yellow magic laced bullets can do at close range, but you don’t dare risk hitting him in the process.

The look on your Don’s face is almost pitying. “SANS YOU WILL REMOVE THIS FILTH FROM MY SIGHT. REMOVE HER DIRECTLY TO THE GOOD DOCTOR.”

Sans doesn’t flinch but you can see the way he’s truly working to suppress the monster in his grasp. No one else here has gravity magic except the Boss, as far as you know, but you can’t let him do this alone.

“An escort!” you all but shout. “I’ll escort them.”

Boss rounds on you, the cool facade he exuded a second before peeled back enough to press the weight of his bidding into you. It’s all you can do not to clutch at your chest as he drags on your contract.

“DO NOT SPEAK OUT OF LINE, SENTINEL. YOU ARE NOT ABOVE CONSEQUENCE.”

“She will  _ Dust _ him!” you shout back.

The air is devoid of a breath, of a movement, so Boss’s hand connecting with the side of your face rings loudly in the cramped space. You think you hear a crack. Your left ear is ringing, and the left eye you were already having trouble with sports a jagged cut above it from one of Boss’s tapered talons. Automatically your hand lifts to your face to feel for blood but you stop it halfway up when his other hand lands on the other side of your face.

Boss never shows his eye lights, never has, but you feel the weight of his gaze on you like a piano dangling above your head. 

“UNDYNE! ACCOMPANY SANS AND THE SENHORA. HALF OF YOU WITH THEM. THE OTHER HALF WITH ME.”

“Yes, sir!” a chorus of voices ring out. Toriel’s snarl cuts beneath the sound like the roll of the waves on the shore in a storm.

“AND YOU.” Boss’s voice would demand your attention if it didn’t already have it. “WILL REMAIN WITH ME, SENTINEL.”

**Notes for the Chapter:**

> [┬┴┬┴┤ ͜ʖ ͡°) ├┬┴┬┴ i post a lot of undertale stuff here](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> ...uhhhhhhhhh oh. What do you think is gonna happen to you now, Sentinel??


	20. The Slipstream Beneath Your Feet

You don’t move. You don’t break his gaze and he doesn’t look away as a flurry of activity follows. Combined with Undyne’s brute strength, the half returning to Safe House 5 are able to wrangle Toriel, brimming with too much EXP, into one of the vehicles.

The half of the contingent that remains with you feels stiff. You can feel they want to fidget but don’t dare.

“CARS. NOW.”

“Yes, sir!”

Boss’s hand locks around your bicep and drags you along with him. You follow him willingly but his stride makes it almost impossible to keep up. Every one step of his takes over two of yours. That hand forces you into the backseat of the closest car. As you tumble to the floor, you can hear the wail of a police siren in the distance, but it’s cut off when he shuts the door behind him.

Alone in the car, your sense of self-preservation spikes, as does Boss’s anger.

“I SHOULD DUST YOU NOW!” Boss exclaims, his hands digging into the carpet on either side of your head. His body is contorted to bend around the backseat in a way that would look unnatural if you didn’t know he was a monster. “HOW DARE YOU ACT INSUBORDINATE AGAINST ME! AND TO BE SO STUPID TO REVEAL ANY SORT OF LOYALTIES APART FROM YOUR CONTRACT WITH ME!”

So, Boss had definitely noticed something between you and his brother. Not that you’re surprised in the slightest. Your outburst truly was ill-advised. Normally you can hide any emotional connection whatsoever with ease; it’s saved your ass on missions countless times.

You’d really stepped in it this time.

“YOU HAVE PROVEN USEFUL THIS LAST YEAR, SENTINEL, BUT DO NOT DOUBT YOUR TRANSGRESSIONS WILL SPELL PAIN FOR YOU!”

“But-”

His right hand grabs the left side of your head, his talons poking into your scalp and cheek, one dangerously close to your eye. The thumb presses into your jaw to keep your mouth shut, and to also cut off part of your airflow. You’d wanted bruises from Sans, and he’d obliged, so Boss’s grip is more painful for it. 

The pressure increases as Boss’s body shakes in anger. “YOU HAVE COST ME MORE THAN YOU CAN REPAY, SENTINEL. YOU SHALL BEGIN TO REPAY THE DEBTS YOU CAN. TODAY. IMMEDIATELY.”

Without your consent your Soul slips free from your chest as Boss flicks the wrist of his free hand. His body has settled further into the floor so his knees trap your legs together, his ankles pressing down on your shins to keep you in place. You know struggling is idiocy and don’t even try. Your traitorous mind reminds you of how delicious it was to be held down by Sans. But this is your Don. And he has your Soul inches from his grip, and could crush you down to single digit HP without effort.

The contract, and your feeble sense of self-preservation, bids you to be still.

As always, you can’t move your gaze away from your Soul when it is outside of your body. Monsters don’t initiate encounters with humans anymore, not like they did the first few years out of the Underground. They aren’t effective enough. But staring at what is essentially all you are never stops.

The color is less important than the light shining off of it. In the dark, tinted windowed car, with Boss leaning over you, it’s blinding. So bright, you can barely see the streaks of vantablack Void that clings to it like the veins on a leaf, but you know they’re there. You’ve seen them enough times that they’re burned into your memory. The color that it was when you were a child, a blood orange that had faded with time and the more LV you gained, is long gone. All that is left is the dark red thread you can clearly see connecting your Soul to Boss, a crystalline shell the shape of a heart, and the black of the Void.

A bump in the road makes the car shake enough that your floating Soul is slammed into the hand hovering around it. You and Boss flinch. His grimace is something you didn’t expect. 

Sucking air as greedily as you can through your nose, Boss’s hand still restricting your head and jaw, you blink through the pain that mimics getting slammed into a wall. If a Soul could bruise then yours would though hardly any HP was knocked off. 

Intent is everything, and while Boss did not mean to touch your Soul at that moment, you could feel in that flash of connection that he is pissed. Oh, so pissed. 

And maybe not handling his new EXP as well as he thinks.

**Notes for the Chapter:**

> [tumblr is a place for fun and friends namely me please talk to me](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> So...you've seen your Soul. What do you think?
> 
> ~~also i promise our fave bone boy has more speaking lines very soon~~


	21. The Safe Deposit

Keeping Toriel contained is difficult, to say the least, and the ride back to the Safe House is tense. If Sans didn’t need to focus completely on his former Dona, he might have allowed himself to worry more about those left behind at the docks. But to show weakness now would be to die and he has a few things he needs to do before he Dusts.

And one of them will be dunking on Asriel the next chance he gets.

Sans has never trusted the crown prince, for good reason, and he knows that sentiment is returned tenfold. Back in the Underground the child caused more harm than good. No one but him seemed to remember the time he spent as a soulless flower and the bright eyed child that carried him in their hair. Gaster, of course, was the only one who could stand to hear their name, but it would send him into Void fits if they discussed it longer than a few words.

“undyne, hold her a sec,” Sans mutters as the group returns to the Safe House. He wishes he could have teleported, but he doesn’t dare use it for that far a distance before his own siphoning with Gaster.

Undyne grips Toriel under her armpits, getting help from a couple of the others present to hold her steady as Sans opens the Safe House combination lock. The pressure activated code is simple for him to complete without thinking, his magic exactly tuned to this sort of security. 

It’s a mad dash to the bunker for the entire group, some taking the stairs rather than join the group restraining the Dona in the elevator.

Toriel at this point is seething and not struggling. Sans doesn’t remove his eye lights from her. He can taste the force of her anger in the air even without his gravitational hold on her Soul. So focused on keeping her steady and avoiding her gaze, Sans misses the way Undyne watches him closely. 

The two of them have never been close except for their equal loyalties to the Boss. A breaking point occurred Underground when the three of them conspired to remove the King from his throne, his LV turning into a slow and dangerous Haze, something most of the citizens ignored. Sans appreciated her action then and appreciates her logic and tactical approach now.

“Don’t let him Dust them” she says, the words forced through her teeth as she clenches her jaw. 

Sans glances away from the blue-encased Soul before him to catch her gaze for a moment. He doesn’t want to say anything in front of the Dona. The beginnings of her Haze are more prominent now.

But, he knows exactly what she means, and acknowledges her with the barest nod and narrowing of his eye sockets. It’s nearly insulting that Undyne would need to say that to him but he recognizes the dual concern on the two left behind.

As focused as he has to remain on Toriel, Sans is nearly vibrating with the magic in his body demanding that he needs to be  _ somewhere else right now _ . When he moves through the Void in shortcuts and calling out his attacks, it’s deliberate. A traverse to another place in time where he wants to be, each movement is calculated in a mind more accustomed to quantum physics and mechanics than anyone should be. But, the moments the Void flips the coin and drags on him, incessant, pleading, it’s difficult to ignore.

Undyne and the others handle Toriel into the room with the other monsters who left before who were close to Haze. Gaster is bent over one of them with his hands gripping their chin. He looks up at the commotion entering his lab and does not ask questions until Toriel is strapped to a free table.

In the commotion, Sans ducks out of the room, rubbing at his sternum to try to alleviate the acidic burning in his Soul. Maybe...it’s worth the risk to shortcut back to them? The burn grows stronger like a crow of triumph, a plea to do  _ exactly _ what he thought to do.

EXP bubbles under the surface of his invisible skin, raising his body temperature and blurring the very edges of his vision. He knows himself. He can handle this, accept the next LV, and do what the Void demands.

He blips out of sight before anyone can stop him.

**Notes for the Chapter:**

> [_to the tune of secret tunnel_ GARBAGE FIRE! GARBAGE FIRE!](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Sans what are you up to??? ~~I mean, I know? BUT LISTEN I JUST~~


	22. The Graceless Turning Point

Boss drags your limp body up from the floor and throws you into the seat opposite him the best he can in the cramped space. Without his hand on your head and throat you’re able to take your first full breath in several minutes, and you don’t waste the chance.

“SO EAGER TO PROVE YOUR WORTH,” Boss sneers, his hands gripped tightly into his femurs, talons cutting through the expensive material. 

Your Soul revealed more to him in that brief connection than you thought. You wonder if he knows you saw how much he’s struggling against a Haze.

“Yes, sir,” you choke out. 

As much as you want to put your hand to your throat to massage the new bruises that mix with the mottled scars from the taser and Sans’s teeth, you resist. You’re in a cramped cage with what could amount to an enraged animal. No chances should be taken.

Belatedly you notice the lack of your pistol, it’s weight gone from your holster. Though you can’t see it you know the weapon modified by Doctor Alphys is somewhere on Boss’s person. This makes you more apprehensive than you’d admit to him, ever. You  _ trust _ Boss. Even after the last forty eight hours trying to convince you that your place is precarious and you should run, like you used to, like you always did, you stay fast. 

“AS YOU ARE AWARE I MUST RETURN TO THE GOOD DOCTOR,” Boss says. “THIS...I DID NOT SUSPECT THE HUMANS WOULD BE WEAPONIZED AS SUCH.”

“Purple magic,” you say quietly.

The switch between nearly choking you out and strategizing is something you’re intimately familiar with. The tone invites comments, but you still must be careful. A twitch of a finger. A longer exhale. Small things help you toe the line with him. 

“CORRECT. YOUR REPORTS WERE ACCURATE, AS WAS YOUR ASSESSMENT OF THE LIMITED TIME WE HAVE.” 

Pausing to wipe away a touch of blood orange magic from his brow and tucking the kerchief back in his pocket, Boss glares out the window at the shining waters of the bay passing by. You keep your eyes trained on him.

“ARE YOU PREPARED FOR ANOTHER ASSIGNMENT, SENTINEL?”

Your name is said with far less force than the last few times it’s left Boss’s lipless mouth, but there is still weight along your contract at it’s sound. “Yes, sir.”

“I INVOKE THE CONTRACT. YOU MAY NOT DISCUSS THIS MISSION WITH ANYONE EXCEPT MY BROTHERS AND I.”

A light glow of his magic surrounds Boss’s hand as he says this, waking up one of the conditions of your connection.The mist of magic settles from him onto your contract thread, racing to your Soul. Eyes fluttering shut, you feel your crystalline Soul absorb the magic greedily and seal the command.

“SANS AND I BELIEVE ASRIEL TO BE PART OF THIS MESS. A ROOT OF THE PROBLEM, IF YOU WILL.”

You’re almost startled into a laugh. A pun? From Boss? If he notices his wordplay he doesn’t acknowledge it, so neither do you for your own safety. You know what the taste of his ire feels like and have seen him exact it on Sans many a time in retaliation for his puns. A sharp throb rises in your cheek to remind you of your new mark from his slap.

“THIS STINKS OF HIS INTERFERENCE,” Boss continues, his hands back to pressing into his thighs. “NO ONE SHOULD HAVE KNOWN YOU WERE MOVING TO INFILTRATE THE HUMAN MOB. SELECT FEW WERE AWARE THAT WAS YOUR MISSION AT ALL. AND, THE WAY TORIEL HAS RESPONDED TO MY ACTIONS AND HER NEW EXP, IT RAISES MY SUSPICIONS AS WELL.”

You nod in agreement, and take a moment to rub at your neck, since Boss seems to be leveling out somewhat. Right now you’d even take Grillby’s caustic version of healing magic, if only to get rid of the feeling you were still being choked. Now that you are paying attention, you can feel the same discomfort in your Soul. You chalk that up to the fact one of Boss’s hands grips your contract fiercely between his talons.

“What’s next, Boss?” you ask against the pain in your throat.

Boss presses a release button in a console next to him. Three vials appear and roll into his hand, the glass tinkling against his bones. Each one is no bigger than your pinky and holds a powdery substance you are very familiar with. 

Freely given Dust, mixed with a special stimulant.

He rolls all three into your outstretched hand and you immediately open the first, tipping it into your mouth before you can think about what you’re doing. As you swallow the chalky mixture you shudder, the uncomfortable itchy feeling of rapid healing washing over you from head to toe. It won’t remove old scars, but it takes away most of the pressure and burning from wounds you’ve obtained the last forty eight hours or so. The other two vials are slipped into your shirt’s breast pocket.

The car slows to an almost stop by the time you can swallow without tasting it. Boss still hasn’t spoken, but you don’t ask again, waiting for him to respond. You’re far from any safe house location you know, the bay stretching on one side of the car and the edge of old city on the other.

“FIND ASRIEL.” Boss says. His eye sockets bore into your face for a moment before he grabs you by the collar of your shirt and throws you from the vehicle in one motion. 

Picking yourself up off the gravel on the side of the road, you hear his last order before the car peels away like a bat out of hell.

“AND BRING HIM TO ME!”

**Notes for the Chapter:**

> [tumblr is where i live](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Boss punning? Asriel mentions? Dust? What is even happening, Sentinel, what's gonna happen to you next?????


	23. The Thief in the Light

Their perch is perfect to watch the entire rumble without getting spotted.

Flurries of activity beneath them are over almost before they begin. Their eyes easily track the movements of each monster and human before them, a skill born out of necessity. 

They won’t admit it hurts a bit that the judge doesn't notice them, though. He always does. Unless he purposefully is ignoring them? If so, he will pay dearly, in this timeline or the next. That detail is of no consequence to them. 

No matter the appearance of his outside form, his Soul is always the same. Always calling to them.

One body in particular catches their eye, and not only because of their proximity to the skeleton. The new human explains everything they need to know in the way they move. Weilding a pistol with yellow bullets, they are a terror, as vicious as any monster in the Underground that believes it is kill or be killed. They should know. The Soul beneath their sternum bears enough scars for thousands of lifetimes. 

Each movement the human makes is precise, deadly, and graceful in the way that proves some skills are born not taught. As the only human on the side of the monsters, they stick out like a sore thumb to the onlooker. The one perched atop the buildings and observing sees so much of themselves in this fighter. 

It doesn't make them hate this other human any less.

Standing in the cool spring air rising off the bay is rejuvenating after so long in the dark of the Void. The trespasser in this world takes a deep breath, filling the lungs in the body made of flesh and bone they chose to cover themselves with in this world. Variations on a familiar theme, of course, but better suited to blend into this pre-apocalyptic place.

Glee, a feeling that coats them inside and out, rises in their Soul as they watch the car leaving the battlefield stop. The flash of a bony hand catches their eye as it shoves that human out of the car, then drives away. It’s not the hand they’re looking for, but it will suffice. 

_ Just a bit more patience _ , they think to themselves, monitoring the labored movements of the new human as they get to their feet and sprint for cover.  _ He’ll come to them. _

_ And then I can kill him. _

**Notes for the Chapter:**

> [T U M B L R](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> ¯\\_(ツ)_/¯no apologies¯\\_(ツ)_/¯for the short chapter¯\\_(ツ)_/¯guess who?¯\\_(ツ)_/¯hehehehe¯\\_(ツ)_/¯


	24. The Gravel in Your Palms

Goddamnit, Boss.

It took less than thirty seconds for you to stand and sprint to hide in the dilapidated buildings near the bay, your hands fisted and pumping at your sides to move you faster. Standing out in the open could spell your death faster than the firefight you were just in.

But of course, he knew that when he shoved you out of a barely-not-moving vehicle. The tightness in your chest near your Soul is now more from catching your breath. Leaning over in the shadows of a building that was abandoned decades ago, you flick your eyes around for the telltale concrete arch that is above most entrances to the service tunnels under this part of the city.

As angry as you are you hope he gets to Gaster before his Haze begins. You wish you had a way to contact Sans to warn him, to maybe shortcut his brother to get there sooner, but your phone was damaged beyond repair by magical tasers.

You spot an entrance to the tunnels and jog to it, keeping an eye on the perimeter for anyone who could have spotted you. There’s nothing in your line of vision, so you shove your shoulder into the crumbling door, rustling it out of the hinges so you could break in.

In the darkness of the sloping hallway you allow yourself a brief moment to grip your head in pain. The Dustmix had helped your situation immensely but the sting of permanent damage remained.

Your feet carry you forward, away from the door you’d put back as best you could to hide your trail. Losing the cops after the firefight was far too easy to make you feel comfortable. Undoubtedly there would be officers down here with you, so the faster you moved, the better. Picking direction is simple, as part of the path is caved in when you try to turn left. Sunlight peeks in as the morning outside fully blooms. Like a vampire skittering away from the light, you turn tail the only direction you can go.

Pieces of the stones and debris from the side of the road fall out of your skin as you rub your hands together. A piece of glass or a stone cut a hole near the knee of your trousers when you landed, and the fabric rubs uncomfortably on the small cut with each step. Your empty holster hits your side with ever jogging step, reminding you with each collision that you are all but weaponless, and you curse Boss again for leaving you vulnerable. The excuse of a Haze is not strong enough. 

He’s testing you. Not that you didn’t expect this, even when you shared that relatively subdued conversation in his office back at the Safe House. Had that really only been twelve hours ago? So much had changed. The persistent heat at the center of your chest reminds you of that. 

Damn Boss and his new mission. You need to talk to Gaster as soon as you can. And Sans. Oh, if he knew something would happen to your Souls when he fucked you then you are going to give him what for the next time he’s in arm’s length!

And yet…

And yet you can still feel the looming presence of something bigger on the horizon.

You reach a place in the tunnel where the only light is from the cracks in the grates and open manholes above your head. Power isn’t directed through here from the main grid unless necessary in emergency. This part of the city is only used by the mobs now, mostly firebombed out decades ago when the families on the surface first tried to push the monsters back Underground. More symbolic than anything now, the Dark Quarter only houses the occasional vagrant and a few colonies of rats.

So, when a voice calls your name behind you, you’re on alert immediately.

The outline of a person about your height stands several yards away in the direction you came from. They don’t move for a moment, and you can’t make out their features enough to tell if they are friend or foe. At first you’d hoped it was Sans by the pitch of their voice, but it was the concrete echoes playing tricks on you.

A smile breaks through the gloom. No human’s smile glows like that, not any that you know, but the teeth are short and blunt. The figure takes two paces forward.

There was a window of time where you could have, should have kept going. You should have run. You have a mission after all, don’t you? Right? Or do you? How clear is a command to find a monster if you don’t have an idea where he is.

The longer you stare at that smile, the less you’re worried about anything you should be doing. It’s more important that you’re here. Besides. This feels familiar. Like it’s supposed to happen.

Two glowing red eyes shine above the smile, beckoning you forward through the gloom.

**Notes for the Chapter:**

> [a gateway to a garbage universe ~~tumblr~~](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> I got some really good guesses on the last chapter for whose perspective that was in...not telling just yet buuuuuuut I feel like this chapter will support some theories. ¯\\_(ツ)_/¯


	25. The Deferential Dona

There are many in this ‘verse Gaster wish were more like they are in his, and Toriel nears the top of his list. Watching her Haze slowly fade away soothes his Soul, but the fact she allowed herself to get that close meant things are not as stable here as they could be.

His mind drifts to you as he works. As soon as Sans, Undyne, and the few family members with them, arrived with Toriel in tow he noted yours and Boss’s absence. With his head clearer than it has been in hours, the pull of the Void all but sated by the amount of EXP siphoned into it after the rumble, he allows himself to think of more dangerous ideas.

Thoughts like wondering why the Void affected him so much today, of all days.

And why Sans would not come near him in the lab. Gaster could feel the call of your Soul, as well, but did not realize Sans could until he saw the skeleton shortcut out of the bunker. It is obvious to him that something happened between the two of you, even without seeing your Soul, though he is unsure if that affected him as well. Gaster is certain you’re not consciously aware of the connection between yours and-

Toriel takes in a huge shuddering breath as Gaster’s hands slowly, delicately, coax the last few EXP away from her and into the Void. The shudders through her fur subside. Her eyes flutter open a moment later and find his easily, red meeting a mismatched pair of orange and blue.

“Doctor Gaster,” she says, her voice rough from the growling tearing through it before. “Thank you.”

“You are welcome,  _ mia regina _ ,” he says, giving her a rare smile. She does not flinch or bristle at the epithet, rather, she returns a glimmer of a smile. “That was very reckless. How are you feeling?”

She scoffs and drags herself to an upright position, leaning back heavily on her elbows. The woman towers over him while standing and meets his gaze when reclined this way. 

“Do not overstep your boundaries, good Doctor. You still have not located my son.”

It is Gaster’s turn to bristle. “Not for lack of effort on my part, my  _ queen. _ Your son is proving slipperier than a moldsmal in Waterfall.”

“I doubt even my son can hide in the Void forever.”

“No one can hide there forever,” Gaster snaps back, turning away to set his instruments into their cleaning chambers. Filaments of light scan around the metal and glass tools to cleanse away Toriel’s magical signature, so they can be used on the next monster close to Haze. “The initial reports stated he and Guy, that rabbit monster, were unharmed and taken to another Safe House. Grillby was headed there late last evening after the Sentinel -”

Toriel growls through her teeth. Gaster ignores her.

“- was collected and returned for healing. He reported through the regular channels that they were present when he arrived.”

“My son is missing,” Toriel insists, swinging her legs off the table and rubbing at her chest. “I’m aware of what the reports state. And far be it from you to take things at face value, Doctor.”

“If my queen would be so kind as to allow me to complete my explanation.”

Heavy silence fills the lab between the two sole occupants. Neither look at the other.

Without thinking of it, Gaster starts to thumb the crack below his left eye. He knows intimately how long it is, since he monitors it daily, and his tumble had resulted in another few micromillimeters of breakage. It would not do to allow his emotions rise to the point of damaging himself further.

“Asriel is strong willed but is weak to the call of the Void,” Gaster states matter-of-factly. “He was not ambushed. He preyed on the weakened emotional state of Guy and another monster to accompany him on a raid to the human family’s underbelly following the loss of Felix. Foolish boy. Whatever happened, he was not prepared, and those with him are lucky to be alive. All signs point to his departure from the Safe House to be of his own design.”

“I know this,” Toriel snaps, moving to stand and fix the clothes draping over her formidable form. “You’re not telling me anything that helps me, Doctor.”

Gaster frowns to show his own failing patience, then drops his hand away from his wound to face Toriel. “Asriel did not return to the Void alone, my queen. He has no means to command that place between. He had assistance. Who would he follow so willingly into that heinous place?”

The change in Toriel’s body language, even with her back turned to him, tells him all he needs to know. She understands. Gaster catches the motion of Undyne just outside the lab door, watching the two of them through a glass window, but unable to hear a word exchanged.

“Senhora Dona,” Undyne says as she opens the door. Toriel standing from the examination table was enough invitation for the Captain to enter with barely a knock to announce herself. “The Boss has arrived. He asks that you wait for him in your office.”

“Thank you, Undyne,” Toriel replies, allowing herself to be lead from the room. She throws one last hard look at Gaster before she rounds the corner, a look schooled to appear deferential and unconcerned, but Gaster knows, and her response to his question confirmed it. He understands.

The anomaly has returned.

**Notes for the Chapter:**

> [r l b m u t](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> ~~guess what i am kind of freaking out because i don't have tomorrow's chapter finished yet and usually i am three chapters ahead on this halp~~


	26. The Near Miss

The salty air off the bay fills Sans’s magical lungs as he lands heavily on top of the building he fought on scarcely a half hour ago. Toriel is safely in the confines of the lab, and he can feel his brother’s magic working to correct her Haze even at this distance. As risky as it can be when his Soul is reshaping itself to the next LV, he’s kept his tether to the Void more open than normal, and the resonance of EXP getting dumped into its greedy maw is difficult to miss.

But he has to filter out the gluttonous cries of pleasure from the inky blackness and focus on another call, another tether through the Void.

There’s Boss. He’s always the easiest to find, even at rest, traveling further away from him and closer to the Safe House and a solution to his own struggle against the EXP gained today. Sans’s hands twitch with worry and the desire to rush back to his brother’s side but resists. Boss will soon be surrounded by monsters who can help him and would not think to hurt him, though the same could not be said for Sans. He knows the others still don’t like him or the way he’s almost always around Boss. 

Sans doesn’t give a fuck. He’s watched Papyrus - Boss - die too many times in other timelines to care what they think.

And then there’s you. That call between your Souls after you’d ignited an unignorable Soulfire within him. It’s a tether as thin as a fishing line but a hundred times as strong between you. He can tell you’re close but isn’t sure where, the connection warping and turning throughout the surrounding space. 

Does he regret what happened? No. He’s too selfish for that. But he does regret how and when. 

No one deserves to be connected to him like this, bound between your Souls, and he suspects you don’t have a clue what this means. He’s weak. Even as the next LV settles over his Soul like a heavy veil, he doesn’t feel his HP budge an inch. Double digit LV and his HP didn’t have the decency to be anything but a measly two. Two hit points. That’s all he had.

And someone like you, with your beautiful crystalline Soul and powerful human form, did not need to be held back by him. 

The scent and feeling he’d been searching for finally creeps up meet him. It’s a rush of sensation after trying to pick it out from the myriad of smells all around him. Under the reek of gull shit, putrefying seaweed caught on the shoreline, and the still present tang of human blood, there’s the fetid stench of determination.

“motherfucker,” he curses under his breath. 

Slipping through the Void as easily as some slip on their caps, Sans takes a shortcut to the ground where the scent is leading him. A grate meant to allow excess rainwater to drain directly into the bay instead of flooding the overgrown parking lot is a beacon of the invisible mark he’s looking for.

His first instinct is always to shortcut as close to his target as possible, but something in the magical tension below him warns him to wait and assess. Not always his best plan. Hesitation means people die. 

And he won’t risk that. Not when he can feel you down there with the fucking anomaly.

**Notes for the Chapter:**

> [_sean connery voice_ my tumblah](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Hey! So thanks to my lovely Discord pals doing some writing sprints I'm a couple chapters ahead again! Thank goodness for writing sprints.


	27. The Resonance

**Summary for the Chapter:**

> Some explanations of soul contracts, including the one between you and Sans.

Soul contracts are strange, all things considered, no matter how they’re formed.

The first kind is made willingly, between two parties that have full control or knowledge of the desired outcome. Most of the monsters in the family hold one of these to the current Don or Dona. The current state of the family is unique that the contracts held to their Bergentrückung should have automatically transferred to Toriel or his son, Asriel. 

Neither were present at the time of his passing, though physical presence is not always necessary for a transference. Across the Underground in the Ruins, Toriel had felt the weight of a dozen or more Souls weighing down on her own. Through the Void, Asriel’s damaged Soul was called through to take up part of that mantle, his body forming from the Dust of his father in the throne room. And the rest moved to Boss even as he sat shaking, absorbing the EXP of the fallen king.

The second kind forms between Souls out of necessity. A mother bonding with her child, a physical manifestation of her unconditional love. Lovers bonded in marriage, something that can start as the first and be braided into something deeper. 

A third contract is the one Gaster can see connecting you and Sans. It’s call is potent, to anyone looking for it, a resonance keeping you tethered through space and time. 

He sits quietly on his - well, he sees it as a perch - within the Void. The highest level of the place between universes, a relatively safe place to observe without interference. 

The conscious bodies, whether made of flesh or magic, housing the Souls in this type of contract do not need to be willing participants. Like metal shavings called towards a magnet, neither party has a say in the matter. If the two puzzle pieces get too close, they will automatically reach out and form a contract between them.

Gaster has seen this happen between Sans and the anomaly hundreds, thousands, of times in other timelines. In other universes. He had never been present for the creation of the contract, and did not initially understand that was the disturbance in the Void that caused him to collapse in the lab. Now he understands. 

Speaking to Toriel today put puzzle pieces into his vision that were previously missing. Memories he suppressed and thought discarded to the Void forever returned. How blind he had been the last two decades. Was it longer? He is not sure. 

The image of Toriel coming to him, drenched from pouring rain and clutching a limp figure to his chest, is something he is not sure how he forgot in the first place. His mind wanders to that night the longer he spends in the Void. It seems here is the only place he can call on all of his memories. He knows as soon as he steps out again he won’t recall a bit of this.

Toriel begged him to find the lost pieces of her son within the Void, essentially begging him to bring her son back from the brink of death. The glitter of her husband’s ashes mixed with the rainwater on her body. Ultraviolet light nearly blinded him when she released the bundle in her arms on the operating table he had then.

Perhaps he was too sentimental, he considers to himself. The Toriel in the universe he originates from will never get to see her children ever again, adopted or biological. Faced with the opportunity to give this Toriel what her Soul so desperately craves no matter the universe or timeline was too strong. Too tempting. He should have learned to not take so much from fate’s hands, to put the burden of choice on his shoulders. 

As much as he wanted to think that at one time, he is not a god.

Gaster’s Soul feels heavy in his chest as he hears the deep thrum of the contract before him getting strained. He doesn’t want to leave the Void, where all pieces of himself assemble neatly. Once he steps back into MF-3 he knows he won’t remember enough to stop himself from continuing down a wretched path.

But he has to try, doesn’t he?

Gaster takes one more longing look at the dazzling crimson thread that ties Sans to you, and follows the familiar tear into MF-3.

**Notes for the Chapter:**

> [_break dances into view_ come hang out on tumblr](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> So, I predict this story will be going on for a couple more weeks at least, but probably not past 50 chapters, so now is the time to ask questions. What do you want to know about Sentinel's past? Sans? Gaster? Boss? ANYthing about Universe MF-3????? Hit me up in the comments, buddy.


	28. The Anomaly of MF-3

**Summary for the Chapter:**

> Your boy encounters someone he doesn't want to see.

“frisk.”

“Sans.” The creature tilts its head to the side, that grin almost glowing in the gloom, teeth reflecting the dark red of his magic back at him. “Or, should I call you Red? That’s your name here, isn’t it?”

Sans tries not to respond to that name, the one tied to his Soul like an anchor on a ship, but he crushes the pack of cigarettes in his pocket. He works to focus on this moment. Any hesistence can mean death, and the way your Soul is tied with his now, would spell yours, too.

So when he sees you collapsed against the brick wall of the tunnel clutching your side, he’s less angry and more...fearful. The death call works both ways, after all. He just never expected yours to be his undoing.

But if he’s still alive, that means you are, too.

“how are you here?”

“Could ask you the same thing, smiley trashbag,” Frisk says with a lilting cadence, the glint of the knife in their hand steady and taunting. “But you’re stalling. Just like you always do.”

The slide through the Void to avoid the knife is automatic. It’s a dance he remembers. Or, his Soul does, since it’s practiced this fight countless times in countless ways. The shortcut takes him a little closer to you, but the brat notices and tries to step in the way again.

Another shortcut. Another dash of the knife, wielded like a shot sword. 

Each step feels like the ripples on the surface of the bay when a stone is thrown in, the waves of his actions reaching far beyond this cramped tunnel under a broken city. All he sees is in a film of red, his magic filling his good eye socket, focusing his energy on stopping this anomalous bastard from causing havoc. His suit feels restricting and he doesn’t flinch when the fabric rips to allow him more room to move. But when a line of his ribs are exposed as Frisk’s knife gets too close, he takes his next shortcut out of reach.

As long as he keeps this up, he can keep them distracted, and keep you safe. Nothing is more important right now.

He’s so focused on avoiding that gleaming knife that he nearly misses the thrum of magic running from his Soul to yours and back again, a bullet train on a track back and forth between you. If he knew he could stop to think about it, he would, but he can’t. Just...one more hit, trap them in bones, maybe? No, the feedback loop coming from all of his other selves tells him that won’t hold them off long enough.

_ then what will, you useless assholes? what good is a multidimensional connection if _ -

“Talking to yourself?” Frisk says with a cackle, stepping back away from him and scrambling on top of a pile of warped boards that likely washed up during a storm into the pipes. Their body moves in ways it shouldn't and he can see the way the Void pulls at the edges of them each time they twist and turn. “I haven’t seen you this far gone since I visited the universe where you slaughtered the entire Underground and ate their Dust!”

Sans hacks at the thought, his invisible tongue heavy in his mouth at the thought of  _ eating _ Dust from monsters he’d killed. Freely given Dust tasted wrong enough without LV getting involved. Though, ripping out the throats of the goons what attacked you did feel  _ divine _ so perhaps it’s another thing entirely when your victim is a different species...

Frisk doesn’t allow his mind to wander for long. The knife is back to hacking the air next to, above, or below him as he dodges and sends volleys of bone attacks through the space to try and land a hit. Damn them for choosing a space like this. In his past, it was hard enough to summon the Blasters in the Judgement Hall, barely enough room to summon more than one or two at a time from the Void. Here it’s impossible for one to fit let alone attack the dodging child without hitting you. What he needs is -

The idea slams into him like a freight train, and he can feel the distinct hand of one of his other selves planting the notion in his head before disappearing again.

What he needs, is space. A hell of a lot of it. And he knows just where to get it.

With a roar, he raises his hands up, his body rising to the top of the tunnel, before he brings them down with a colossal slam, ripping open a gaping tear into the Void.

**Notes for the Chapter:**

> [tumblr is my city](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> ̿̿ ̿̿ ̿̿ ̿'̿'\̵͇̿̿\з= ( ▀ ͜͞ʖ▀) =ε/̵͇̿̿/’̿’̿ ̿ ̿̿ ̿̿ ̿̿


	29. The Memory Lapse

“How’s that, darling?” Mettaton coos. “Your shoulders are an absolute nightmare!”

“GOOD, I PREFER THEM NIGHTMARISH,” Boss gouches, leaning over his desk with dozens of sheets of paper spread out around him. 

The four armed robot behind him leans a little more to take a sneaking glance of his own. Two of those hands keep busy working out tension along the column of vertebrae showing out of the top of Boss’s shirt. There are floor plans, diagrams of human and monster Souls, and too many things to catch at once. But his fiber optics make short work of the information, snapping pictures to store away for later use.

Boss tenses again as his thumbs get closer to the base of his skull. Though Mettaton is sure he didn’t hurt him, he backs away from the Don and says, “Darling, what is it? Did I do-”

“SILENCE!”

Mettaton springs back further to press himself against the wall. Like a shot, Boss stands from his desk, the movement scattering pages around him. Fists clenched at his sides, Mettaton can see the way he’s shaking with fury with his ultra-sensitive optics. Without notifying his Don he sends a quick distress signal to Doctor Alphys down in the lab, and nearly sighs in relief when she answers immediately. Part of him recognizes that it would take a significant amount of power for the Boss to dismantle and destroy him before Alphys had a chance to reach him and extract him from the situation. He knows Alphys is clever enough to bring Undyne with her if she can.

On cue, there’s a knock at the door, but Boss is already halfway to it. He whips around to bare a snarl at the robot still pressed against the wall. If Mettaton had a human throat, he would have swallowed out of fear.

“I’LL DEAL WITH YOU LATER,” Boss promises before reaching for the handle and twisting it open hard enough to startle the pair on the other side. 

Alphys sprints to Mettaton when Boss brushed passed her and down the hall. Undyne looks between the Doctor and her leader, and decides to tail the Boss. 

“W-what happened?” Alphys says as she checks his chassis for damage and her fingers send little tendrils of yellow magic towards him.

He brushes her away gently. “Nothing, thankfully, my dear. But he showed signs of being...unstable. Haze-like symptoms like you warned me. We didn’t even get to the part when I got to take off his clothes.”

Alphys makes a face while Mettaton pouts.

“H-he probably felt Doctor Gaster come back,” Alphys says as she completes her check-up, finding nothing wrong with her creation except a few gears and gyros spinning a little too fast in response to Mettaton’s fear. “I don’t think he asked him to go into the V-void, but I saw his tether when I w-went into the lab. He w-was in there for a while.”

Mettaton hums to show he’s listening, watching over the Doctor’s shoulder and turning up the sensitivity in his ears to make sure they weren’t getting overheard. Alphys is very clever, but forgets sometimes that the family is not above taking advantage of their own for personal gain.

“I wondered if that could be it,” he muses quietly, when he can tell the closest monster is far enough away to not catch what he’s saying. He wishes Alphys had closed the door behind her, but this is still Boss’s office, and as volatile as he’s acting after that human ambush, minimal chances should be taken. “The last time Gaster did something like this without checking with Boss first -”

“Boss a-absorbed Jerry,” Alphys finished for him.

Mettaton chuckles, a strange metallic sound as his sound system crackles with static. One of his hands absently strokes the fins on the back of Alphys’s head in a soothing motion. “Jerry was in the wrong place at the wrong time as always. That’s his own fault.”

“S-still,” Alphys says, leaning a little into the touch of her best friend. So little comfort exists in the world of monsters, it’s hard not to preen whenever it’s given. “Gaster shouldn’t have been poking around there without Boss knowing, not after he almost Hazed. Everyone seems to forget he exists until he comes back and that just makes Boss so mad when he suddenly remembers Gaster and I get so nervous when that happens I don’t want to get absorbed by Boss just because I was in the wrong place at the wrong time, too, and-” she takes a deep shuddering breath to stop her hushed rambling - “Just d-don’t tell anyone I told y-you about that!”

Mettaton uses one arm to hug her close for a brief moment before letting her go again, walking out of the office with his back ramrod straight to preserve his image. Looking over his shoulder he beckons the Doctor to follow him as he shuts the door behind him, leaning in to whisper,  “Your secret is safely stored in my circuits, my dear.”

**Notes for the Chapter:**

> [drop on by for the best undertale garbage i can find](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Something about getting snowed in at home makes me wanna write Undertale. Send me prompts on tumblr, beauties.


	30. The Deep Breath

**Summary for the Chapter:**

> Some answers, and a few more questions.

You feel weightless. The sensation is unlike swimming, or being carried by gravity magic. You feel as though you have no mass or substance at all. A consciousness, existing outside of your body.

There’s a sensation you recognize as opening your eyes, but there’s nothing to see. Not blackness. Not darkness. Just...nothing.

Your lungs open to take a deep breath but no air fills your lungs, though you don’t feel like you’re suffocating. Breathing and blinking are just human physical reflexes, after all, and don’t mean anything in the Void.

It’s been a very long time since you’ve spent this long in the Void. You carry a piece of it inside of you, something that initially drew you to the monsters with a magnetic, undeniable force, nearly driving you mad until Gaster taught you how to slake its thirst.

All in all, waking up in the Void isn’t as jarring for you as it was twenty years ago during your first journey through. Only when you’re in this space can you put all the pieces together, bring all the data in front of your face. Wisps of memory soak into your brain that is there but not there like cigarette smoke curling up and all around you. 

Dimly, you’re aware of two other presences nearby. The Void is vast, so you’re positive there are others here, but they’re too far away for you to acknowledge, or vice versa. Instead your consciousness is swallowed up by the almost overwhelming flood of memories begging to be let in.

The scent of dirty rain water pouring off a rooftop in a city choked with smog rushes up to meet you. It’s your earliest memory, besides the feeling of bruises from punishments for taking more food for yourself from the dingy kitchen, and the gnawing feeling of hunger. Memories of a white-faced man appearing in your room at the orphanage fill you with curiosity instead of fear, and you remember what your tiny hands looked like in his as he grabbed them to pull you through. Gaster. Doctor Gaster.

The memory of the first time you ever saw a monster from this universe makes your Soul ache. Toriel’s face rises with hope, and falls to a despair deeper than you’ve ever witnessed, her mouth forming the words, “ _ They are not the right one. _ ”

Your tumultuous ride through your lost memories is interrupted by the feeling of a skeletal hand holding your arm. You weren’t aware you still held your human shape, and as soon as you do, you regret it as the pain returns with it.

“hey, sweetheart.”

Sans’s voice reverberates through your head instead of getting picked up by your ears. “Sans? Why are we in the Void?”

“i...heh,  _ we _ just needed some space and time to work things out.”

“We?”

“Yes,” says a new, and very disgruntled voice.

You recognize it and feel your metaphorical hackles rise. You can’t see or feel your body but you are aware of the presence of the...thing from the tunnel that used a mesmer on your Soul, throwing you off balance, and then  _ stabbing you in the gut _ . Without knowing where Sans is, you try to put yourself between him and the little demon, the soul contract between you humming more strongly the closer you get to him.

“What the fuck are  _ you _ doing here?” you snarl. 

You really wish you had a weapon, but here in the Void, damage can’t really be dealt or given. It’s truly a neutral ground. Chaotic neutral, really, you think with a bitter taste in your incorporeal mouth.

“ _ What the fuck are you doing here _ ?” the voice taunts back. It sounds like a child, but you’re not above showing a kid what for if they talk to you like that. “Damn, you’re just a high-strung mess, aren’t you?”

“frisk.” Sans’s voice is dark with warning, with a huge dose of exasperation mixed in.

“What, it’s true!”

“frisk, would ya shaddup and tell them what ya told me?”

You get the impression that the demonic child, Frisk, is throwing up their hands in defeat as their voice says, “Fine! Your universe is fucked, okay? Someone found the metaphorical plug and is just letting all the sense drain out of it into the Void.”

“Excuse me? A plug?” you ask.

“Like a drain in a sink? This universe is all the water in the sink and someone decided it was a good idea to go messing with the tear that connects this place to all the others and take things in and out that don’t belong here.” Frisk is definitely mocking you now, and you don’t care for the tone on this kid who thought stabbing you was a good idea. “Sound like anyone we know?”

The last bit was directed at Sans who you can feel bristling somewhere beside you. “don’ look at me, bucko, that’s not my gig here.”

“Gaster,” you say between clenched teeth. It feels wrong to give the kid the satisfaction of an answer, but you don’t have the patience for this. Though you have all the time in the world here in the Void, you need to make sure to not lose your grip on the place you dropped in from.

Your answer placates Frisk enough for their tone to settle a little. Since you’re in the Void, you start to recognize that this demon across from you is more than what cornered you in the tunnel, it’s too much Soul in one body, a stronger version of whatever hurt you. And, just like the way you regain your full self in this world, the pieces the Void has slowly sapped away from you through excessive LV, you can tell the same is true for Frisk and Sans. You’re more in here. You get to take back the parts the Void took away.

But as soon as you return, you aren’t sure if you will keep those vital portions of yourself, so you grit your teeth and force yourself to continue speaking. “What does this mean for us, then?”

Frisk laughs, a crisp sound that reverberates in your head and feels sadder than anything they’ve said yet.

“Simple. We reset.”

**Notes for the Chapter:**

> [ɹlqɯnʇ](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> I've been spending time on Markiplier's Discord server the last couple days, so if this story gets more chaotic, let's blame that okay? Deal.


	31. The Crown Prince

Asriel toys with a frayed hem on his shirt and thinks back on all the shit decisions that lead him to this moment.

The cramped cell smells like it’s close to the bay, the mixture of salty air and a heavy scent of grease and oil that coats the back of his tongue gives it away. He can hear the waves, too, if he concentrates. All of this is familiar and would be comforting, if he thought anyone else knew where he was.

His mother is going to kill him.

Scratch that, she’s going to make him live and suffer through her displeasure.

Not that he doesn’t deserve it, he thinks dejectedly to himself. She didn’t deserve the way he’s acted the last few years. Returning to a bipedal form instead of living the rest of his days as a little golden flower hadn’t granted him any real sense of maturity. His mind remembers all those years spent living in the Underground, all the resets where he tried to help scared little children escape the hell of a world that believed  _ kill or be killed _ .

Foolish, then, to think the outside world would be any different.

He only succeeded in saving one of the children but something felt wrong about them, as if they knew too much. Oh, sure they had more determination than he ever did, and were able to override his magic without knowing they were doing it at first. But...something was wrong.

And he fell for it. Again.

The heavy scrape of one of the human family’s tasers against the cement floor makes him start to shake. Guy, huddled up in a corner next to him, holds his arms more tightly around his body. Asriel scoots to cover him more, his much larger body helping shield the monster that did not deserve to get caught up in his mess. 

Maybe...maybe he could open a portal into the Void. He’d succeeded for a while before...before Aaron dissolved. He can already tell by the massive oncoming headache that no one would remember his name or his existence except for him. That was the price of the Void, it seemed. Another Soul. Asriel shudders again as he considers the risk this would put Guy into.

No. He won’t let another monster die because of his cowardice.

“Le petit prince,” a human says in a horrible mockery of a French accent. His shoulders roll under his shirt as he plays with the baton. Coils of purple magic loop at the end like a cat of nine tails. “Where’s yer mama, huh? Where’s the rescue squad?”

Asriel lets his lips curl away to reveal the sharp rows of teeth and two sets of fangs set into his maw, hoping the low light would paint him in a grisly visage. “Fuck off, asswipe.”

“Tsk, tsk. That’s the wrong answer, ya lil’ shit.”

Standing, Asriel blocks the goon’s view of Guy tending to his wounds and increased EXP in peace. Spending a moment in the Void had helped the bunny monster deal with some of that oncoming Haze, but it wasn’t enough. There were too many humans dead by their hands after their failed ambush. Asriel just needs to buy him a little more time before it takes hold.

“Little?” His horns scrape the top of the cell before he reaches his full height. Forming from his father’s ashes assured he grew into a broad and intimidating specimen. “I’d like to see you say that to me without the bars of a cell between us.”

Some of the gusto the goon showed off deflated from his shoulders, but he didn’t stop toying with the taser. Asriel wishes he recognized the magic, and can’t figure out how the thing is getting charged in the first place, though he has a sickening hunch. Magic needs something to fuel it, after all.

“I wish I could kill ya,” the man says, taking a few steps further back towards the door at the end of the room of cells. “But you’re more use to the boss alive.”

He’s gone without another word, so Asriel falls back down to inspect Guy. The bunny monster breathes deeply in through his nose and out through his mouth as he lays limply on his side on the floor. Asriel brings a hand close to his arm, but Guy recoils automatically when he gets close. 

“Guy, can you hear me?” Asriel says, settling back so he can sit cross legged on the floor next to him.

“Mmmph,” the monster responds. “Fucking hurts.”

There isn’t anything Asriel can say to that without feeling like a fraud. His Soul practically aches to be filled with more EXP, so he has no idea what sort of pain a monster with too much feels like. 

As he sits there quietly fretting over what the next move should be, he feels a tug on his Soul. It’s...familiar, though he hasn’t felt it in years. 

“Chara?” he whispers.

Guy is too far into his own head to notice Asriel move away to stand at the far corner of their cell and reach his dinner-plate sized hand towards a seemingly uninteresting wall. If he had, he would have noticed the way that clawed hand slipped into the concrete like the surface of a murky lake, returning covered in specks of a black goo-like substance.

He also would have noticed the way a mountain of a monster slipped through the cracks of reality and out of the holding cell.

**Notes for the Chapter:**

> [there is a place of productivity but this is not it](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> I figured I danced around Asriel for long enough. In this story he doesn't match what I see of him visually if he came back from being a flower. That is more accurately represented in the [growth spurt au](http://potoobrigham.tumblr.com/).
> 
> _also can i have a little mini freak out over this story getting over 3k hits???? holy shit????_


	32. The Debt of Determination

**Summary for the Chapter:**

> How you came to MF-3.

It’s impossible here, but you could really go for a cigarette. A responding thrum across your soul contract tells you that Sans feels the same way.

“crushed ‘em before we came in here, though,” he says, answering the unspoken question. “so i don’t have any for when we leave.”

Mental barriers didn’t really exist in the Void, especially not for two creatures whose Souls greatly depended on them. So, you can’t be upset he essentially read your mind, and that privacy is limited.

A shimmer in the corner of your vision alerts you that he’s shifting before you can feel him press against your back. This sort of physical intimacy is what your Soul screamed for outside of this liminal space between universes, so you’re not going to look a gift horse in the mouth. After a little turn, one of your arms wraps around him to pull him closer, his head coming to lean on your shoulder. 

Your gut still clenches in pain every few moments but you ignore it. It’s easy to do here.

Somewhere far enough away that you can’t even see their Soul shimmer, Frisk sits and waits. It’s more meditation than waiting, honestly, an attempt to pull the broken pieces of themselves together. You can understand that. You’re attempting to do the same.

You wonder if that’s what Sans is doing, too.

“won’t work for me, sweetheart,” he mutters against you. You can feel the slight movements of his mouth even if you can’t quite make out the shape of him, but his voice is still inside of your head. “you’n the kid can try but there’s nothing for me t’gather up. no loose ends.”

You frown. “What do you mean?”

“i’ve always been part of the void. every single one’a me across these universes. means i don’t really forget when i’m outside’a it.”

“Then why-”

“both of ya are humans,” he says, his shoulder shrugging against your ribs. “not s’posed to be here. like the kid said, gaster messed around with things he shouldn’ta.”

A bitter pill slides down your throat as your hand absently searches for the top of his skull. Your hand hits his sleeve on the way up, and you feel those little cufflinks in his sleeve, which makes your throat tighten with emotion. 

“Does that mean you regret this? That we weren’t ever supposed to meet?”

Sans stiffens beneath your arm until your fingers start stroking his skull, tracing scars and divots gently. One of his hands reaches over to grab yours, the one laying loosely on your lap. He brings it up to his thin lips and presses the jagged ridges of his teeth against your palm. 

The touch sends a shiver through you. His hand behind you, the one settled against your hip, digs its claws slightly through your clothes in response. His voice is gruff and slightly muffled by your hand when he speaks again.

“never. i’ll never regret you.”

You keep stroking his skull and trying to ignore the way his touch makes you feel. 

In the darkness of the Void you can’t see it, but you feel the way all the pieces of your memories stitch together. The longer you’re here in this place that transcends time the heavier your Soul feels. It’s not blue gravity magic affecting you. The crystalline casing of your Soul is slowly refilling with its original color. A bright, vibrant red of determination. 

It hurts like a motherfucker the fuller it gets, like more and more weight getting stacked on your arms even after you’re carrying too much. There’s no telling if it will even stay when you leave the Void again. But you ignore the pain in favor of focusing on the skeleton in your barely visible arms.

You understand how Gaster could be confused, then, when the queen tasked him with finding the other instances of her lost children. Asriel reformed through the ashes of his father and a hell of a lot of his borrowed determination leftover from Doctor Alphys's barely sanctioned experiments. So, when Gaster appeared in this timeline for the first time decades ago, Toriel jumped on the chance her beloved Chara existed somewhere else, too. 

She was not above ripping an otherwise unknowing child from their bed thrice over to try and find them. In her mind the only logic was, find the spark of determination that lived there and it  _ would have to be _ her child. Nevermind the ones who were not and were cast aside. You know the other children before you were thrown back or died minutes after leaving the Void. So, to stop the weight of another dead child on his conscience, Gaster tacked on some of the Void to your Soul and drained it of determination before you could take your third breath of oxygen in MF-3.

The universe you came from was already crumbling when he found you. Your soul shone brightest among the other dying starts, a beacon of magic determined to stay alive despite the destroyed fabric of the universe around it. The only reason your world was destroyed in the end was because you were removed from it. Nothing else could hold it together, and with it’s only hope removed, like a poorly stacked bonfire, it fell to ruin.

Much like the one you called home now threatened to do.

The question you ask yourself now, as you feign recuperation in an unforgiving Void, is if you are the reason MF-3 is staying together - or the reason it’s falling apart.

**Notes for the Chapter:**

> [tum-tum-tumblrrrrrrrrrr](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> So. I'll be real with y'all. I still love this fic and wanna finish it, but it's been 32 straight days of posting chapters, and interest has kind of waned for it overall. You guys still interested in daily updates or nah? I can't improve if you don't give me feedback.


	33. The Ternion of Trespassers

**Summary for the Chapter:**

> Taking another step forward.

“Time means nothing here, but that doesn’t mean we should stay.”

You glare daggers at Frisk, but don’t deny it. Under your arm, Sans starts to pull away, your only comfort in this realm of darkness. He doesn’t move far though, keeping hold of your thigh with one of his hands. You want to lace your hands through his but will settle for this.

“what’s to say we’ll remember any of this when we leave, frisk?” he says, the pressure on your thigh increasing a bit. “we got no way to know you won’t try to kill us again, or if you’ll lemme heal them.”

Frisk, though you can’t see their face, definitely rolls their eyes if their tone is anything to go by. You really want to smack this little shit into next week.

“Don’t you think I thought of that? We might as well take a leaf out of Chara and Asriel’s book though.”

Sans bristles next to you immediately, a spark of his soul visible for a moment in the otherwise encompassing darkness as it flares with anger. “y o u  a r e  n o t  a b s o r b i n g  m e.”

“Relax, asshole,” Frisk says, but you do catch a hint of wariness in their voice in place of the childish confidence. “That’s not what I meant. Believe me, I like this even less than you, but that little soul contract the two of you have going on? We need to make one, too. For all three of us.”

Your cheeks heat up and stomach turns at the idea of just  _ how _ this contract seemed to be made and the idea of doing anything like that with this demonic thing...well, you’d honestly rather suffer another stomach wound. 

“Ugh, not like  _ that _ , sicko,” Frisk says. “Keep those nasty thoughts to yourself. There are other ways to make soul contracts, stupid. I don’t have a Don or Dona since I don’t belong to this backasswards world, so I can connect myself like to the two of you, like an ornament hanging off the soul contract you already have. Since, I mean, if one of you die then it won’t matter what happens to me anyway.”

The way they say it sets your blood to ice. “What do you mean?”

They shrug. “I’ll fade, or at least the piece tying me here will. The Frisk that was here, the one that helped to break the barrier and free the monsters when they probably shouldn’t have, they died a long time ago. But you know that.”

The last bit is said with accusatory fire, and you rise to the challenge. Sans’s claws dig into your thigh slightly when you say, “Then where do you belong, you little shit?”

“Nowhere,” Frisk says with finality. “I’m the shadow of all the Frisks that failed and didn’t have enough determination to come back and reset the world. I’m the ones that let Chara take over and destroy those worlds, and we’re trying to make things right in the other ones.” They take a deep breath before continuing. “And you were someone like me in your world, but Gaster took you away before you had a chance to save anyone, bringing you here to take the place of the queen’s dead kids.”

“How do we make it right, with the reset then? Won’t it try to send me back to a world that doesn’t exist anymore?”

Frisk pauses to consider your question, and you start to get antsy before long. The only anchor you have is Sans’s hand on your leg, his clawed thumb pinching tighter every now and then. 

“As much as I hate to admit this...we need to actually get Gaster in here so we can ask him. He caused this shit-mess, he should take responsibility in fixing it, too.”

Sans stiffens next to you. Dimly through your connection you’re aware of an enormous feedback loop happening in his Soul, exhausting him past his usual lazy standards. You want to ask him what it is, what it means, but Frisk is right.

You don’t have time.

Standing, a wholly unnecessary action that just makes you feel like you’re stalling without wasting time, you pull Sans up with you and keep him close. The weight of his hand on your opposite hip is as comforting as feeling a weapon there. You’re still pissed at Boss for leaving you weaponless.

“Will it hurt?” you ask as Frisk steps closer, the smudge of their Soul you can see floating somewhere near your gut. 

“Shouldn’t,” they answer. “And it should make healing you after we get out of here easier. More Soul magic involved.”

“I don’t use magic-”

“I do, you idiot,” the anomaly snaps back harshly. “And Sans cannot die, which means  _ you  _ cannot die.”

You want to retort but you want to get moving faster than that. Sans is far too exhausted by the loop in his Soul that reaches beyond the Void to do more than snarl at the demon child. Boss’s orders to find Asriel would have to wait, anyway, since you’d need to get to Gaster as soon as possible. And you figure, after a reset if the crown prince is still missing then you can go looking for him. After most of this shit is undone. If it even matters.

The ritual to bind themselves is mundane, all things considered. One moment you are two twined Souls watching a third move closer, and the next moment that Soul hangs like a ghastly Christmas light on a red thread.

“That’ll do,” they mutter. Their Soul wriggles a little to settle itself. “You ready?”

You’re not. You move towards the open tear back into MF-3 anyway...

...just as another Soul enters the Void behind you.

**Notes for the Chapter:**

> [i reblog and post good shit here](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Thank you to those who reached out regarding my last note. Since I had a chapter ready for today I figured I would keep the daily schedule!
> 
> However, from now until the end of the story (let's say another 10-15 chapters or so?) I'm going to move to every other day. That way I can keep putting quality work together until the end instead of rushing it out! Make sure to let me know any characters you'd like to know more about in MF-3 since I have a pretty set idea of how this will go but would love to answer any questions in story that you have.


	34. The Doctor's Reticence

“WHAT ARE YOU DOING, GOING THERE WITHOUT STRICT PERMISSION FROM ME?”

“I am working under your direct orders, brother.”

“EXCUSES! YOU KNOW HOW...PERTURBING IT FEELS TO SUDDENLY REMEMBER YOU ALL OVER AGAIN WITHOUT WRITTEN WARNING FROM MYSELF!”

Gaster stands and listens to the Boss berate him with the appropriate amount of chastisement apparent on his face, but stood his ground nonetheless. Keeping up appearances is important in each ‘verse he visits. But he will not fold to any individual on any plane if it is not what gets him closer to his goals. 

The usefulness of this family is closer to reaching its grisly conclusion, and he will not stand in the way of their self-destruction.

He endures another half hour of upbraiding from his Boss quietly. His assistant’s creation eventually comes to collect him so that he can strategize and contact his other wayward brother. If Gaster thought the Boss was pissed at him for doing something out of turn, the rage he sees Boss direct towards the report of Sans not staying after the raid is nothing.

The yelling stops halfway through the hallway, much sooner than Gaster expected, perfectly timed with a sudden flare of pain in his time wound. He focuses on the shape of the pain blooming in his skull and recognizes it quickly.

Ah. So Sans was in the Void again?

Typically when his void-brother shortcut anywhere he could feel a faint echo of pain, not dissimilar to the descriptions he was given of human toothaches. This was longer, and he knew that if he asked anyone around him if they’d seen Sans, they would start to get ill if they tried to think on him.

A new flare of pressure joins it, one he rarely feels in this universe. It is the calling card of the anamoly, in any universe, but it feels double layered. As though...there are two…

Gaster blinks once. Then twice. A wicked smile blooms over his head as his skull tics to the side. Unknown to him, he’d lost more than he’d gained the last time he’d entered and left the Void.

Well. The Boss is already mad at him. Why not go back in and say hello to his void-brother and the human pet he had claimed for himself?

**Notes for the Chapter:**

> [a portal to my void](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Gaster, you should have checked thyself before you started to wreck thyself.
> 
> A short one today, guys! But with the way the outlining is for the next few chapters, this one didn't fit as part of a larger chapter. Happy Atlantale day to those attending!


	35. The Broken Compass

**Summary for the Chapter:**

> Two characters meet in the Void.

**Notes for the Chapter:**

> _slowly drops chapter and somersaults away_

The Void parts like curtains on a vast stage, welcoming him back with open arms.

Asriel still feels uncomfortable here. He knows living things don’t belong here. This place is meant to recycle the Souls that fall in after the living body falls down or passes on. Even with his impressive height and breadth, he feels small here. Microscopic.

Breathing doesn’t matter here but he still moves his chest up and down in a way to calm himself. 

“Chara?” he calls again. 

The echo he thought he felt here is faint, and disappears even as he tries to grab onto it.

“They are not here, Asriel.”

The crown prince can feel his body move, even if he can’t see it. “Doctor Gaster?”

There’s a sigh that comes from his left and all around him at the same time. A warm boney hand rests against his shoulder. The sensation is spine-tingling in this wretched place, but he can tell it’s meant to be comforting.

“I am sorry to see you here, my friend,” the Doctor says. “I fear the walls holding your world together are starting to crumble and fade. If you are able to walk freely into this space between just as the anomaly, Sans, and I do...there is little hope for the universe’s survival.”

Asriel is quiet as he listens to Gaster. He can feel his feet moving beneath him as the gentle grip the doctor has on his arm moves him through the Void. Memories he doesn’t understand pound at his head. It’s worse than deja vu...he feels everything his soul has ever experienced and does not know how to handle the sensation.

The doctor’s voice pulls him back for a moment. “Time is short outside of this strange place, my friend. Are you prepared to help me?”

“What do you need me to do, doctor?”

Motion ends as Gaster’s hand moves away from his arm. Asriel can feel the doctor’s hesitation, a fine thread of light or sound or something deeper than even feeling passing in the aether around them. The lines of reality feel blurred.

“I need you to make sure that, no matter what, no living part of myself returns to MF-3.”

“Pardon?”

“My dear boy, I do not belong there anymore. Or anywhere. I have...made many mistakes. I am better off to stay here, to spend my days in a realm where I cannot hope to hurt others.”

Asriel’s Soul starts to ache in his chest. “I don’t understand.”

“You will. In time, you will.” 

Gaster starts to walk away, his voice fading. Asriel reaches out through the Void to try and grab Gaster the way the doctor rested his hand against him. He needs the anchor as much as the doctor right now.

Instead, a pocket back into his world opens behind him, pulling him back through to the safehouse, and the waiting arms of his mother and cruel eyes of the Boss.

**Notes for the Chapter:**

> [dis a tumblr link :D](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> I am back for a bit! I was able to smash out a few chapters in this one this weekend so you get basically a chapter every other day for a bit. I still don't think this will stretch further than 50 chapters total, so we are in the home stretch, guys!!!!!


	36. The Muddled Memories

**Summary for the Chapter:**

> Three leave the Void.

All of you clutch your hands to your heads as the last creeping tendrils of Void power slip away. The tear mends itself with a sound you feel more than you hear. It digs into the ground and the air around you in a staticky, grinding tone to seal the Void from this world.

“I don’t like the sound of that,” you say through clenched teeth.

“The world is literally collapsing,” Frisk says.

Hearing their voice outside of that world sends ice through your veins. You can still feel the punch through your gut from their knife, the cold slip of your blood as it rushed towards the wound and out of you. Memories piece together slowly, and you know there are details you’re missing, but your instincts say to stay away from this little demon.

They’re tiny. Smaller than what their voice would suggest. Shaggy dark hair falls like brambles on their head and shoulders. You wonder the last time it was brushed, if ever. This small detail unexpectedly makes your heart pang with understanding, a sense of camaraderie for another person that was not taken care of probably doesn’t know how to do that for themselves. You let that feeling go immediately. Their skin carries an almost jaundice-yellow hue, the sunlight above your heads doing nothing to help the sick pallor.

The worst part of all are the blood-red eyes watching your every move.

Sans stands between the two of you, his shoulders pressing back into your chest to hold you up. You were so intently staring at Frisk that you didn’t realize you were stumbling. One of your hands rests on Sans’s shoulder to steady yourself.

“I’m not going to attack you again. But I _ will  _ make you move.”

“yer in no place to be threatenin’ us,” Sans snaps back. 

The shoulder beneath your hands is tense with anger. The gold fang in the corner of his mouth glitters in the sunlight. His protective actions stir something deep and primal in you, but there’s too much happening inside and around you for you to pay much attention to that.

“I’m the only one with a knife and who...can find…” You and Sans watch as their eyes go blank and their mouth goes slack. Muttering under their breath, they clutch their hand to their head again. “Damnit. Who is the key? It’s a doctor…”

You mutter the only name you can think of attached to that title. “Alphys? Are you talking about Alphys?”

Frisk shakes their head and the shaggy locks bounce on their head in an unhealthy mass. 

“if we’re going, we need to travel separate,” Sans says. “can’t have too much determination in one place.”

The little demon agrees with a curt nod, their hands back at their sides. “Correct. The wounds in reality will get worse.”

“an’ if we don’t see you in -” Sans pulls out his gold pocket watch for a fraction of a second to check the time and press a button “-two hours, we’ll go back into the Void to meet up.”

“Reasonable.”

You don’t like the way their head tilts to the side as they look at you. An itch in your chest gets worse the longer they stare. It’s like they’re toying with the connection between the three of you.

“Would you stop?” you hiss, your fingernails digging painfully into the skin of your chest.

Frisk grins with more teeth than they should. “Just making sure I’ll find you, that you can’t give me the slip.”

“get outta here, tramp,” Sans gruffly says. He’s angled just enough that you can see his eyelights roll in exasperation.

You don’t know if you’re imagining the small amount of reluctant affection you can hear and feel in his voice. You don’t think you are. You don’t want to think about it at all.

In the space of a blink, Frisk is sprinting off in a slightly diagonal direction towards the safehouse where Alphys is. You’d given them the location in the Void, and though some of what happened there is missing from all of your memories, that seemed to stick.

You wish you could remember the rest. Something is missing but, it must not be that important.

**Notes for the Chapter:**

> [tumblr is basically a black hole](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Alphys???? What about G̺̩̞̜̪̙ͅḁ̼͓͈͚st̼̯̤̩e҉͓̺͎̘͉̲r̟̬?


	37. The Admission

**Summary for the Chapter:**

> A moment alone.

“ready to go, sweetheart?”

Sans’s voice is soft, quiet compared to the call of gulls above your heads.

Several minutes have passed since Frisk left, and the two of you waited to give them a good head start. You know they could use the Void to jump, or maybe they’d run the whole way. Their body doesn’t look or act like a normal human, after all, so there’s no telling. The two of you can flash there in a blink anyway.

“I don’t know yet,” you say. 

You’re trying to be honest with him, and with yourself. You don’t even know how you’re standing right now. On a human, your grip on his shoulder would be bruising, but he isn’t complaining. Sans is being excruciatingly patient with you right now. It’s out of character for him, and that makes it all the more noticeable to you. Sans is lazy, yes, and sharp tongued, and never patient. Except with his brother, the Boss.

And now you.

“s’alright, let’s check out that wound first, yeah?”

You nod silently. There’s a tug on your Soul you recognize as coming from him now that you’ve gotten used to the feeling of being connected. He’s trying not to show how worried he really is.

It’s easy to slip back into the warehouse where Frisk ambushed you, the wall crumbling open with a maw wide enough for the two of you to stand by side. Small clouds of dust rise beneath your feet as you walk together inside. You’re far enough from your puddle of blood from the stabbing that you can’t see it. You can still smell it, though. That’s a new sensation, too, one you wonder if it’s connected to being bonded to Sans.

Sans gestures for you to sit on one of the wooden beams laying on the ground. In a gesture of uncharacteristic geniality, he removes his coat so you can lay down on it.

“lift yer shirt,” he says gruffly.

You obey, the fabric already mostly tugged out of the top of these damned borrowed pants anyway. With the grim way things are shaping up, you wonder if you’ll ever wear clothes that fit again, and the thought makes you giggle manically.

Sans stops what he’s doing immediately. “what, am i ticklin’ ya or somethin’?”

“No, it’s just…” you trail off and try to catch your breath. You grab onto his hands and move them back to your stomach. You don’t look down at your wound as he inspects it. “It’s just all of this, happening so fast...you’d think the whole universe hangs in the balance because of our bond or something. It’s ridiculous.”

His bony fingers ghosting over your abdominals, Sans says something so quietly you almost miss it.

“yer my universe, sweetheart.”

Your muscles freeze, except for your mouth that is. “Wh-what?”

Sans doesn’t look at you. His hands move slowly on your stomach around the narrow, shallow gash that landed just short of your kidney. The trace of his fingers is gentler even than necessary.

“s’why i was afraid of being alone with you,” he growls into his collar. You wish he’d look at you, but you’ll take what you can get. “i felt like i had to bond with you since you gave me these goddamned cufflinks. never was the right time. and didn’t want ya to get stuck with a monster like me. ya deserve better.”

You sit up slowly onto your elbows so you can grab one of his hands with yours. Under your touch his bones are on fire and trembling. The tug on your Soul gets stronger until you feel it straining to break free.

“Sans…”

The whimper would make you feel weak in front of anyone but him. His head snaps around to stare at you when his name leaves your lips like that. Your name, not your code name, or ‘sweetheart’, hisses through his teeth. Without warning his lips are on yours.

It’s as rough as the last time your lips met, but with a different sort of urgency moving between you. One of his hands goes to your other side to prop himself up while your lips and tongues war for control. The pressure in your chest is as urgent as the ache between your legs.

Sans does waste time using his other hand to fumble open the belt and buttons keeping him from your most sensitive area. You lift your hips to help him, one of your hands fisted in his shirt. There isn’t much room on the beam you’re laying on, one of your legs dangling off so your foot can support you. It’s needed, since Sans almost collapses on top of you when his fingers slip into your pants to find you ready for him.

“Ah,  _ yes _ , Sans,” you hiss into his lips. 

It’s a struggle to breathe as he moves quickly to find what you need to chase sweet oblivion. The edges of his claws threaten to peek out, but the scratch only makes you move faster against him, desperate for that delicious pleasure-pain.

A different pain interrupts you as Sans presses his arm against you to get more leverage with his fingers. His arm brushes against your wound and you instinctively move away from him.

“let me fix that,” his hoarse voice whispers in your ear.

The hand that was toying with you moves up to press flat against the wound, the fingers still slick with you. Your hips still slowly buck and mourn the loss of his hand even if this is more important than your orgasm. Warmth and red moves from a spot between the two of you down to your stomach. 

Your bond, almost impossible to spot in the dull light of the tunnel you both were hiding in, stitched your injury together better than anything you’d seen Toriel or Grillby accomplish. Far less painful, too.

Red magic isn’t meant for healing, but you wouldn’t know that to see your new bright scar.

“now,” he growls, “where were we, sentinel?”

**Notes for the Chapter:**

> [toomblah](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
>  
> 
> _holy shit more than 4,000 views what_


	38. The Hope of Fools

Limbs akimbo, the two of you slide off the beam and to the cobbled floor. The impact is softened slightly by his coat beneath you, but it still knocks your foreheads together, and you lose your breath as Sans lands on top of you.

It takes you no time to recover. Sans’s hand is down your pants again and your hips are up to move the pants off, your feet shoving your shoes off. Your hands unbutton his shirt. This time, he doesn’t turn you around, doesn’t stop you from running a finger over his collarbones. He doesn’t stop you before your hand is pressed against his sternum, your fingers curling inward.

“fuck!” he curses. 

His face moves to the crook of your neck and his mouth opens wide over your shoulder. The points of his fangs cut into your skin deliciously. 

Inside of his ribcage, the bones are coarse and textured. You wonder if his clothes have made the outside smooth, because it’s slippery in comparison. Your tongue has easy access to his vertebrae so you take advantage of that. The first lick has him groan into you and bite down harder to muffle it. The second, your tongue moving further up towards his zygomatic arch, makes him twist a hand into your hair, only one free to hold him up.

The third makes the magic form into what you want between his thighs. 

As soon as it spawns he’s rutting against you. Your grip on his sternum is an anchor for both of you, and you alternate squeezing the bone gently and rubbing your fingers where you can. It’s like you’re both racing each other to get the other off first.

You’re determined to win.

It’s quick work to shimmy his pants down past his femurs. He wants it as much as you do. Once they’re past his knees he kicks them off to kneel in front of you between your legs. This way, he’s not trying to stay propped above you, and can use the other hand to continue his work between your thighs, one hand still in your hair with an unforgiving grip.

The bright thread of your bond burns between you as he leans over, twisting around your fingers near his Soul and down to your Soul still hidden in your chest. At least, last you knew it was. As you worked to take off as much clothes as necessary, Sans moved his hand from pulling your hair to your chest.

The bright red of his cock fills your vision until the red of your Soul replaces it. You have to stare at it; it’s an automatic reaction. What used to be an empty crystalline shell is full of red, red magic. If it’s Sans’s or your own, you don’t care. 

What’s the difference now, anyway?

Both of you are still aware of your surroundings, clouded as you are by lust, so you fight to keep as quiet as possible as he runs his fingers slowly along first the almost invisible thread then touches your Soul. It’s a shock you can only compare to a combination of all the good feelings you’ve ever had in your life: 

Safety in the monster family, holding Guy close as the two of you huddle for warmth while out on a job, the way Sans looked at you in your party clothes before and after you showed him where you were hiding the carroting wire, Sans calling you sweetheart the first time, Sans touching you, Sans, Sans Sans...

“ _ stars _ ,” Sans groans as he shares the near overwhelming pleasure. “so amazing.”

Your heels dig into the rough cobblestone as you seek any sort of friction between you. Hazed as you are, you beg. 

“ _ Please _ , Red.”

The code name sends a roar of magic through him, and the bones you can see that are already shiny with magical sweat start to shimmer. His mouth moves back to the spot on your shoulder where he’d pulled the shirt completely away to bite down again as much to silence himself as set you off. 

You keen in pleasure as the sharp points of his teeth dig into you, the excess magic on his body mending you almost as fast as he’s breaking the skin. Is the red your blood or his magic? Unclear at this point.

So focused on catching your breath, when Sans moves to line himself up with your more than ready entrance, you gasp at the touch. His fingers had worked you until you were prepared for his girth to slide in with relative ease. Even as the pressure increases inside of you as he thrusts in, the weight of urgency against your Soul starts to get satisfied.

A whispered prayer of  _ yes yes yes _ leaves your lips with each thrust of his cock inside of you. It’s fast, and just as menacing as the first time you did this, but facing him leaves your Souls straining to touch one another’s. Like two ends of a magnet, they repel and repel until something flips and they repel no more. Acting like a snake, the thread of connection between you wraps around your Souls to hug them close in a burst of ecstacy.

You stop breathing for a moment, and you’re sure you blacked out from the unexpected connection. Neither of you were consciously pulling them together, but your Souls knew what you needed. Ultimate closeness before what you both are ignoring.

This could be the end. This could be the last mission either of you make.

But, for now, you indulge in a fool’s hope and hold on a little longer.

**Notes for the Chapter:**

> [tumblrcoin](https://uwa-so-frisk.tumblr.com/) || [sentinel fanart](https://uwa-so-frisk.tumblr.com/tagged/sentinel-fanart) || [ MOBTALE Playlist on Spotify](https://open.spotify.com/user/emilyvergin/playlist/0mvbWBFOAcfxvFsAUKP2DR)
> 
> Hope you all have loved your April Fool's Day/Easter!


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